I have a program that compiles in XCode. In that program, I am taking advantage of stringstream's ability to store values according to the type that they are being assigned to.
Eg) The user inputs a letter, a number, and a symbol separated by spaces in the console. I make a call to getline that gets all three values and stores them in a string. I then create a stringstream with that string's data and assign the values to some variables, a char, an int, and a char in this case. I compile and run within XCode and this works. Then, I take that same file in a terminal and call g++ -o executableName fileName.cpp. Here, I get an error.
Working Example:
main.cpp
#include <iostream>
#include <sstream>
#include <string>
using namespace std;
int main() {
string buffer;
char letter;
int number;
char symbol;
cout << "Enter (letter) (number) (symbol): ";
getline(cin, buffer);
stringstream(buffer) >> letter >> number >> symbol; //The error occurs here
cout << letter << " " << number << " " << symbol << endl;
return 0;
}
I compile and run in XCode:
Enter (letter) (number) (symbol): B 145 #
B 145 #
Program ended with exit code: 0
I compile with g++:
$ g++ -o test main.cpp
main.cpp:14:26: error: invalid operands to binary expression ('std::__1::stringstream' (aka 'basic_stringstream<char>') and 'int')
stringstream(buffer) >> letter >> number >> symbol;
~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~
and then follows all of this:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:789:1: note: candidate function not viable: no known conversion from 'char' to 'unsigned char ' for 2nd
argument
operator>>(basic_istream& __is, unsigned char __s)
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:797:1: note: candidate function not viable: no known conversion from 'char' to 'signed char ' for 2nd
argument
operator>>(basic_istream& __is, signed char __s)
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:804:1: note: candidate function [with _CharT = char, _Traits = std::__1::char_traits] not viable:
no known conversion from 'std::__1::stringstream' (aka 'basic_stringstream') to 'basic_istream > &' for 1st argument
operator>>(basic_istream<_CharT, _Traits>& __is, _CharT& __c)
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:832:1: note: candidate function not viable: no known conversion from 'char' to 'unsigned char &' for 2nd
argument
operator>>(basic_istream& __is, unsigned char& __c)
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:840:1: note: candidate function not viable: no known conversion from 'char' to 'signed char &' for 2nd
argument
operator>>(basic_istream& __is, signed char& __c)
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:220:20: note: candidate function not viable: no known conversion from 'char' to
'std::__1::basic_istream &()(std::__1::basic_istream &)' for 1st argument
basic_istream& operator>>(basic_istream& (__pf)(basic_istream&))
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:224:20: note: candidate function not viable: no known conversion from 'char' to
'basic_ios >::char_type, std::__1::basic_istream >::traits_type> &()(basic_ios >::char_type, std::__1::basic_istream >::traits_type> &)' (aka 'basic_ios > &()(basic_ios > &)') for 1st argument
basic_istream& operator>>(basic_ios&
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:229:20: note: candidate function not viable: no known conversion from 'char' to
'std::__1::ios_base &()(std::__1::ios_base &)' for 1st argument
basic_istream& operator>>(ios_base& (__pf)(ios_base&))
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:232:20: note: candidate function not viable: no known conversion from 'char' to
'basic_streambuf >::char_type, std::__1::basic_istream >::traits_type> *'
(aka 'basic_streambuf > ') for 1st argument
basic_istream& operator>>(basic_streambuf __sb);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:233:20: note: candidate function not viable: no known conversion from 'char' to 'bool &' for 1st argument
basic_istream& operator>>(bool& __n);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:234:20: note: candidate function not viable: no known conversion from 'char' to 'short &' for 1st
argument
basic_istream& operator>>(short& __n);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:235:20: note: candidate function not viable: no known conversion from 'char' to 'unsigned short &' for
1st argument
basic_istream& operator>>(unsigned short& __n);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:236:20: note: candidate function not viable: no known conversion from 'char' to 'int &' for 1st argument
basic_istream& operator>>(int& __n);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:237:20: note: candidate function not viable: no known conversion from 'char' to 'unsigned int &' for 1st
argument
basic_istream& operator>>(unsigned int& __n);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:238:20: note: candidate function not viable: no known conversion from 'char' to 'long &' for 1st argument
basic_istream& operator>>(long& __n);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:239:20: note: candidate function not viable: no known conversion from 'char' to 'unsigned long &' for 1st
argument
basic_istream& operator>>(unsigned long& __n);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:240:20: note: candidate function not viable: no known conversion from 'char' to 'long long &' for 1st
argument
basic_istream& operator>>(long long& __n);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:241:20: note: candidate function not viable: no known conversion from 'char' to 'unsigned long long &'
for 1st argument
basic_istream& operator>>(unsigned long long& __n);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:242:20: note: candidate function not viable: no known conversion from 'char' to 'float &' for 1st
argument
basic_istream& operator>>(float& __f);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:243:20: note: candidate function not viable: no known conversion from 'char' to 'double &' for 1st
argument
basic_istream& operator>>(double& __f);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:244:20: note: candidate function not viable: no known conversion from 'char' to 'long double &' for 1st
argument
basic_istream& operator>>(long double& __f);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:245:20: note: candidate function not viable: no known conversion from 'char' to 'void &' for 1st
argument
basic_istream& operator>>(void& __p);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:740:1: note: candidate template ignored: could not match '_CharT ' against 'char'
operator>>(basic_istream<_CharT, _Traits>& __is, _CharT __s)
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:1506:1: note: candidate template ignored: could not match 'basic_string' against 'char'
operator>>(basic_istream<_CharT, _Traits>& __is,
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/istream:1638:1: note: candidate template ignored: could not match 'bitset<_Size>' against 'char'
operator>>(basic_istream<_CharT, _Traits>& __is, bitset<_Size>& __x)
^
1 error generated.
Is my use of stringstream wrong? (as an aside, Why does XCode allow the code to compile while g++ does not? I thought XCode uses the same g++)
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Here is the full program.
I'm using clang 13 with -std=c++20 -stdlib=libc++.
The error message, not included here because it's extremely long, basically says that the compiler does not even consider the operator<< function I've included here (error is on the std::cerr line near the end of the snippet).
#include <iostream>
#include <string>
#include <unordered_map>
template<typename K, typename V, typename ...Args>
std::ostream& operator<<(std::ostream& os, std::unordered_map<K, V, Args...> const& o) noexcept
{
for (auto const& [k, v] : o)
os << " " << k << ": " << v;
return os;
}
namespace my_namespace
{
struct A
{
std::unordered_map<int, std::string> map{{1, "hello"}, {2, "goodbye"}};
};
A a;
}
int main()
{
std::cerr << my_namespace::a; // error is here
}
Here is the lengthy error message (sorry for not including it earlier):
file.cpp:25:15: error: invalid operands to binary expression ('std::ostream' (aka 'basic_ostream<char>') and 'A')
std::cerr << a;
~~~~~~~~~ ^ ~
/usr/lib/llvm-13/bin/../include/c++/v1/cstddef:141:3: note: candidate function template not viable: no known conversion from 'std::ostream' (aka 'basic_ostream<char>') to 'std::byte' for 1st argument
operator<< (byte __lhs, _Integer __shift) noexcept
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:748:1: note: candidate function template not viable: no known conversion from 'A' to 'char' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __os, char __cn)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:781:1: note: candidate function template not viable: no known conversion from 'A' to 'char' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, char __c)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:788:1: note: candidate function template not viable: no known conversion from 'A' to 'signed char' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, signed char __c)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:795:1: note: candidate function template not viable: no known conversion from 'A' to 'unsigned char' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, unsigned char __c)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:809:1: note: candidate function template not viable: no known conversion from 'A' to 'const char *' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __os, const char* __strn)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:855:1: note: candidate function template not viable: no known conversion from 'A' to 'const char *' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, const char* __str)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:862:1: note: candidate function template not viable: no known conversion from 'A' to 'const signed char *' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, const signed char* __str)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:870:1: note: candidate function template not viable: no known conversion from 'A' to 'const unsigned char *' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, const unsigned char* __str)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:1055:1: note: candidate function template not viable: no known conversion from 'A' to 'const std::error_code' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __ec)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:741:1: note: candidate template ignored: deduced conflicting types for parameter '_CharT' ('char' vs. 'A')
operator<<(basic_ostream<_CharT, _Traits>& __os, _CharT __c)
^
/usr/lib/llvm-13/bin/../include/c++/v1/__random/uniform_int_distribution.h:282:1: note: candidate template ignored: could not match 'uniform_int_distribution<type-parameter-0-2>' against 'A'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:802:1: note: candidate template ignored: could not match 'const _CharT *' against 'A'
operator<<(basic_ostream<_CharT, _Traits>& __os, const _CharT* __str)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:1038:1: note: candidate template ignored: could not match 'basic_string<type-parameter-0-0, type-parameter-0-1, type-parameter-0-2>' against 'A'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:1046:1: note: candidate template ignored: could not match 'basic_string_view<type-parameter-0-0, type-parameter-0-1>' against 'A'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:1063:1: note: candidate template ignored: could not match 'shared_ptr<type-parameter-0-2>' against 'A'
operator<<(basic_ostream<_CharT, _Traits>& __os, shared_ptr<_Yp> const& __p)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:1082:1: note: candidate template ignored: could not match 'bitset<_Size>' against 'A'
operator<<(basic_ostream<_CharT, _Traits>& __os, const bitset<_Size>& __x)
^
file.cpp:6:15: note: candidate template ignored: could not match 'unordered_map<type-parameter-0-0, type-parameter-0-1, type-parameter-0-2...>' against 'A'
std::ostream& operator<<(std::ostream& os, std::unordered_map<K, V, Args...> const& o) noexcept
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:1030:11: note: candidate template ignored: requirement 'integral_constant<bool, false>::value' was not satisfied [with _Stream = std::ostream &, _Tp = A]
_Stream&& operator<<(_Stream&& __os, const _Tp& __x)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:1075:1: note: candidate template ignored: could not match 'unique_ptr<type-parameter-0-2, type-parameter-0-3>' against 'A'
operator<<(basic_ostream<_CharT, _Traits>& __os, unique_ptr<_Yp, _Dp> const& __p)
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:188:20: note: candidate function not viable: no known conversion from 'A' to 'std::ostream &(*)(std::ostream &)' for 1st argument
basic_ostream& operator<<(basic_ostream& (*__pf)(basic_ostream&))
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:192:20: note: candidate function not viable: no known conversion from 'A' to 'basic_ios<std::basic_ostream<char>::char_type, std::basic_ostream<char>::traits_type> &(*)(basic_ios<std::basic_ostream<char>::char_type, std::basic_ostream<char>::traits_type> &)' (aka 'basic_ios<char, std::char_traits<char>> &(*)(basic_ios<char, std::char_traits<char>> &)') for 1st argument
basic_ostream& operator<<(basic_ios<char_type, traits_type>&
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:197:20: note: candidate function not viable: no known conversion from 'A' to 'std::ios_base &(*)(std::ios_base &)' for 1st argument
basic_ostream& operator<<(ios_base& (*__pf)(ios_base&))
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:200:20: note: candidate function not viable: no known conversion from 'A' to 'bool' for 1st argument
basic_ostream& operator<<(bool __n);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:201:20: note: candidate function not viable: no known conversion from 'A' to 'short' for 1st argument
basic_ostream& operator<<(short __n);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:202:20: note: candidate function not viable: no known conversion from 'A' to 'unsigned short' for 1st argument
basic_ostream& operator<<(unsigned short __n);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:203:20: note: candidate function not viable: no known conversion from 'A' to 'int' for 1st argument
basic_ostream& operator<<(int __n);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:204:20: note: candidate function not viable: no known conversion from 'A' to 'unsigned int' for 1st argument
basic_ostream& operator<<(unsigned int __n);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:205:20: note: candidate function not viable: no known conversion from 'A' to 'long' for 1st argument
basic_ostream& operator<<(long __n);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:206:20: note: candidate function not viable: no known conversion from 'A' to 'unsigned long' for 1st argument
basic_ostream& operator<<(unsigned long __n);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:207:20: note: candidate function not viable: no known conversion from 'A' to 'long long' for 1st argument
basic_ostream& operator<<(long long __n);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:208:20: note: candidate function not viable: no known conversion from 'A' to 'unsigned long long' for 1st argument
basic_ostream& operator<<(unsigned long long __n);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:209:20: note: candidate function not viable: no known conversion from 'A' to 'float' for 1st argument
basic_ostream& operator<<(float __f);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:210:20: note: candidate function not viable: no known conversion from 'A' to 'double' for 1st argument
basic_ostream& operator<<(double __f);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:211:20: note: candidate function not viable: no known conversion from 'A' to 'long double' for 1st argument
basic_ostream& operator<<(long double __f);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:212:20: note: candidate function not viable: no known conversion from 'A' to 'const void *' for 1st argument; take the address of the argument with &
basic_ostream& operator<<(const void* __p);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:213:20: note: candidate function not viable: no known conversion from 'A' to 'basic_streambuf<std::basic_ostream<char>::char_type, std::basic_ostream<char>::traits_type> *' (aka 'basic_streambuf<char, std::char_traits<char>> *') for 1st argument
basic_ostream& operator<<(basic_streambuf<char_type, traits_type>* __sb);
^
/usr/lib/llvm-13/bin/../include/c++/v1/ostream:216:20: note: candidate function not viable: no known conversion from 'A' to 'std::nullptr_t' (aka 'nullptr_t') for 1st argument
basic_ostream& operator<<(nullptr_t)
^
1 error generated.
You have provided operator<< for a wrong type there. You gave for the std::unordered_map not for the my_namespace::A. Hence, the compiler can not find a operator<< for my_namespace::A.
You need instead
namespace my_namespace
{
// ...
std::ostream& operator<<(std::ostream& os, A const& a) noexcept
// ^^^^^^^^^^^^
{
for (auto const& [k, v] : a.map)
os << " " << k << ": " << v;
return os;
}
}
See demo
You overload operator<< for std::unordered_map<int, std::string> but not my_namespace::A here.
One way is to overload it for my_namespace::A.
std::ostream& operator<<(std::ostream& os, const A& a) noexcept
{
for (auto const& [k, v] : a.map)
os << " " << k << ": " << v;
return os;
}
Another way is to make A can be implicitly converted to std::unordered_map<int, std::string>.
struct A
{
A() {}
std::unordered_map<int, std::string> map{{1, "hello"}, {2, "goodbye"}};
operator std::unordered_map<int, std::string>() const {
return map;
}
};
I want to support ostream for std::optional<T>. My problem is std::optional<user defined type> is captured by the new function that I have added, but std::optional<int> is not captured.
Inside foo.h, I have the following code
template <typename T>
std::ostream& operator<<(std::ostream& stream, const std::optional<T>& info)
{
if (info) {
stream << *info;
} else {
stream << "None";
}
return stream;
}
Inside types.h:
struct MyType {
...
...
};
inline std::ostream& operator<<(std::ostream& stream, const MyType& my_type)
{
...
return stream;
}
Inside pqr.h
#include <"foo.h">
#include <"types.h">
struct ABC {
std::optional<int> a;
std::optional<MyType> b;
}
inline std::ostream& operator<<(std::ostream& stream, const ABC& abc)
{
stream << abc.a; //commenting this line solves the issue
stream << abc.b; //Printing userdefined structure has no issues
}
Commenting the line
stream << abc.a;
solves the issue. It is so weird that my template code is not captured for std::optional<int>, but captured for my user-defined type std::optional<MyType>. The even weirder part is that both the lines are next to each other in the same file.
COMPILATION LOG:
error: invalid operands to binary expression ('basic_ostream<char, std::__1::char_traits<char> >' and 'const std::optional<int>')
stream << abc.a;
~~~~^ ~~~~~~~
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:219:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'const void *' for 1st argument; take the address of the argument with &
basic_ostream& operator<<(const void* __p);
^
/usr/lib/llvm-9/bin/../include/c++/v1/type_traits:4034:3: note: candidate function template not viable: no known conversion from 'basic_ostream<char, std::__1::char_traits<char> >' to 'std::byte' for 1st argument
operator<< (byte __lhs, _Integer __shift) noexcept
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:195:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'std::__1::basic_ostream<char> &(*)(std::__1::basic_ostream<char> &)' for 1st argument
basic_ostream& operator<<(basic_ostream& (*__pf)(basic_ostream&))
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:199:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'basic_ios<std::__1::basic_ostream<char, std::__1::char_traits<char> >::char_type, std::__1::basic_ostream<char, std::__1::char_traits<char> >::traits_type> &(*)(basic_ios<std::__1::basic_ostream<char, std::__1::char_traits<char> >::char_type, std::__1::basic_ostream<char, std::__1::char_traits<char> >::traits_type> &)' (aka 'basic_ios<char, std::__1::char_traits<char> > &(*)(basic_ios<char, std::__1::char_traits<char> > &)') for 1st argument
basic_ostream& operator<<(basic_ios<char_type, traits_type>&
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:204:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'std::__1::ios_base &(*)(std::__1::ios_base &)' for 1st argument
basic_ostream& operator<<(ios_base& (*__pf)(ios_base&))
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:207:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'bool' for 1st argument
basic_ostream& operator<<(bool __n);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:208:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'short' for 1st argument
basic_ostream& operator<<(short __n);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:209:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'unsigned short' for 1st argument
basic_ostream& operator<<(unsigned short __n);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:210:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'int' for 1st argument
basic_ostream& operator<<(int __n);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:211:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'unsigned int' for 1st argument
basic_ostream& operator<<(unsigned int __n);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:212:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'long' for 1st argument
basic_ostream& operator<<(long __n);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:213:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'unsigned long' for 1st argument
basic_ostream& operator<<(unsigned long __n);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:214:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'long long' for 1st argument
basic_ostream& operator<<(long long __n);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:215:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'unsigned long long' for 1st argument
basic_ostream& operator<<(unsigned long long __n);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:216:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'float' for 1st argument
basic_ostream& operator<<(float __f);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:217:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'double' for 1st argument
basic_ostream& operator<<(double __f);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:218:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'long double' for 1st argument
basic_ostream& operator<<(long double __f);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:220:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'basic_streambuf<std::__1::basic_ostream<char, std::__1::char_traits<char> >::char_type, std::__1::basic_ostream<char, std::__1::char_traits<char> >::traits_type> *' (aka 'basic_streambuf<char, std::__1::char_traits<char> > *') for 1st argument
basic_ostream& operator<<(basic_streambuf<char_type, traits_type>* __sb);
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:223:20: note: candidate function not viable: no known conversion from 'const std::optional<int>' to 'std::nullptr_t' (aka 'nullptr_t') for 1st argument
basic_ostream& operator<<(nullptr_t)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:760:1: note: candidate function template not viable: no known conversion from 'const std::optional<int>' to 'char' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __os, char __cn)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:793:1: note: candidate function template not viable: no known conversion from 'const std::optional<int>' to 'char' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, char __c)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:800:1: note: candidate function template not viable: no known conversion from 'const std::optional<int>' to 'signed char' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, signed char __c)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:807:1: note: candidate function template not viable: no known conversion from 'const std::optional<int>' to 'unsigned char' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, unsigned char __c)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:821:1: note: candidate function template not viable: no known conversion from 'const std::optional<int>' to 'const char *' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __os, const char* __strn)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:867:1: note: candidate function template not viable: no known conversion from 'const std::optional<int>' to 'const char *' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, const char* __str)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:874:1: note: candidate function template not viable: no known conversion from 'const std::optional<int>' to 'const signed char *' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, const signed char* __str)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:882:1: note: candidate function template not viable: no known conversion from 'const std::optional<int>' to 'const unsigned char *' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __os, const unsigned char* __str)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:1066:1: note: candidate function template not viable: no known conversion from 'const std::optional<int>' to 'const std::__1::error_code' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __ec)
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:3895:1: note: candidate function template not viable: no known conversion from 'const std::optional<int>' to 'const std::__1::bernoulli_distribution' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __os, const bernoulli_distribution& __x)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:753:1: note: candidate template ignored: deduced conflicting types for parameter '_CharT' ('char' vs. 'std::__1::optional<int>')
operator<<(basic_ostream<_CharT, _Traits>& __os, _CharT __c)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:814:1: note: candidate template ignored: could not match 'const _CharT *' against 'std::optional<int>'
operator<<(basic_ostream<_CharT, _Traits>& __os, const _CharT* __str)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:1049:1: note: candidate template ignored: could not match 'basic_string' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:1039:1: note: candidate template ignored: requirement '!is_lvalue_reference<std::__1::basic_ostream<char> &>::value' was not satisfied [with _Stream = std::__1::basic_ostream<char> &, _Tp = std::__1::optional<int>]
operator<<(_Stream&& __os, const _Tp& __x)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:1057:1: note: candidate template ignored: could not match 'basic_string_view' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:1074:1: note: candidate template ignored: could not match 'shared_ptr' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os, shared_ptr<_Yp> const& __p)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:1086:1: note: candidate template ignored: could not match 'unique_ptr' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os, unique_ptr<_Yp, _Dp> const& __p)
^
/usr/lib/llvm-9/bin/../include/c++/v1/ostream:1093:1: note: candidate template ignored: could not match 'bitset' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os, const bitset<_Size>& __x)
^
/usr/lib/llvm-9/bin/../include/c++/v1/valarray:4165:1: note: candidate template ignored: substitution failure [with _Expr1 = std::__1::basic_ostream<char>, _Expr2 = std::__1::optional<int>]: no type named 'value_type' in 'std::__1::basic_ostream<char>'
operator<<(const _Expr1& __x, const _Expr2& __y)
^
/usr/lib/llvm-9/bin/../include/c++/v1/valarray:4180:1: note: candidate template ignored: substitution failure [with _Expr = std::__1::basic_ostream<char>]: no type named 'value_type' in 'std::__1::basic_ostream<char>'
operator<<(const _Expr& __x, const typename _Expr::value_type& __y)
^
/usr/lib/llvm-9/bin/../include/c++/v1/valarray:4196:1: note: candidate template ignored: requirement '__is_val_expr<std::__1::optional<int> >::value' was not satisfied [with _Expr = std::__1::optional<int>]
operator<<(const typename _Expr::value_type& __x, const _Expr& __y)
^
/usr/lib/llvm-9/bin/../include/c++/v1/iomanip:362:1: note: candidate template ignored: could not match '__iom_t8' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os, const __iom_t8<_MoneyT>& __x)
^
/usr/lib/llvm-9/bin/../include/c++/v1/iomanip:482:1: note: candidate template ignored: could not match '__iom_t10' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os, const __iom_t10<_CharT>& __x)
^
/usr/lib/llvm-9/bin/../include/c++/v1/iomanip:572:33: note: candidate template ignored: could not match '__quoted_output_proxy' against 'optional'
basic_ostream<_CharT, _Traits>& operator<<(
^
/usr/lib/llvm-9/bin/../include/c++/v1/iomanip:592:33: note: candidate template ignored: could not match '__quoted_proxy' against 'optional'
basic_ostream<_CharT, _Traits>& operator<<(
^
/usr/lib/llvm-9/bin/../include/c++/v1/regex:5238:1: note: candidate template ignored: could not match 'sub_match' against 'optional'
operator<<(basic_ostream<_CharT, _ST>& __os, const sub_match<_BiIter>& __m)
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:1981:1: note: candidate template ignored: could not match 'linear_congruential_engine' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:2451:1: note: candidate template ignored: could not match 'mersenne_twister_engine' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:2772:1: note: candidate template ignored: could not match 'subtract_with_carry_engine' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:2954:1: note: candidate template ignored: could not match 'discard_block_engine' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:3207:1: note: candidate template ignored: could not match 'independent_bits_engine' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:3439:1: note: candidate template ignored: could not match 'shuffle_order_engine' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:3662:1: note: candidate template ignored: could not match 'uniform_int_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:3783:1: note: candidate template ignored: could not match 'uniform_real_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:4073:1: note: candidate template ignored: could not match 'binomial_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:4191:1: note: candidate template ignored: could not match 'exponential_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:4345:1: note: candidate template ignored: could not match 'normal_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:4495:1: note: candidate template ignored: could not match 'lognormal_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:4716:1: note: candidate template ignored: could not match 'poisson_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:4827:1: note: candidate template ignored: could not match 'weibull_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:4946:1: note: candidate template ignored: could not match 'extreme_value_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:5118:1: note: candidate template ignored: could not match 'gamma_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:5254:1: note: candidate template ignored: could not match 'negative_binomial_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:5360:1: note: candidate template ignored: could not match 'geometric_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:5464:1: note: candidate template ignored: could not match 'chi_squared_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:5584:1: note: candidate template ignored: could not match 'cauchy_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:5706:1: note: candidate template ignored: could not match 'fisher_f_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:5822:1: note: candidate template ignored: could not match 'student_t_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:6045:1: note: candidate template ignored: could not match 'discrete_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:6346:1: note: candidate template ignored: could not match 'piecewise_constant_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/lib/llvm-9/bin/../include/c++/v1/random:6685:1: note: candidate template ignored: could not match 'piecewise_linear_distribution' against 'optional'
operator<<(basic_ostream<_CharT, _Traits>& __os,
I want to declare my 2D vector first, then give it a size.
But why I am getting error?
Can anyone explain me?
int main() {
vector<vector<int>> a;
a = vector<int>(16, vector<int>(15));
cout << a.size() << a[0].size();
}
The reason for doing it is that I don't know the size before but after getting the input from the user, I want to give it the size.
Error:
Char 9: error: no matching constructor for initialization of 'vector<int>'
a = vector<int>(16, vector<int>(15));
^ ~~~~~~~~~~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:507:7: note: candidate constructor not viable: no known conversion from 'vector<int>' to 'const std::vector<int, std::allocator<int>>::allocator_type' (aka 'const std::allocator<int>') for 2nd argument
vector(size_type __n, const allocator_type& __a = allocator_type())
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:519:7: note: candidate constructor not viable: no known conversion from 'vector<int>' to 'const std::vector<int, std::allocator<int>>::value_type' (aka 'const int') for 2nd argument
vector(size_type __n, const value_type& __value,
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:572:7: note: candidate constructor not viable: no known conversion from 'int' to 'const std::vector<int, std::allocator<int>>' for 1st argument
vector(const vector& __x, const allocator_type& __a)
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:604:7: note: candidate constructor not viable: no known conversion from 'int' to 'std::vector<int, std::allocator<int>>' for 1st argument
vector(vector&& __rv, const allocator_type& __m)
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:622:7: note: candidate constructor not viable: no known conversion from 'int' to 'initializer_list<std::vector<int, std::allocator<int>>::value_type>' (aka 'initializer_list<int>') for 1st argument
vector(initializer_list<value_type> __l,
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:650:2: note: candidate template ignored: deduced conflicting types for parameter '_InputIterator' ('int' vs. 'std::vector<int, std::allocator<int>>')
vector(_InputIterator __first, _InputIterator __last,
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:494:7: note: candidate constructor not viable: requires single argument '__a', but 2 arguments were provided
vector(const allocator_type& __a) _GLIBCXX_NOEXCEPT
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:550:7: note: candidate constructor not viable: requires single argument '__x', but 2 arguments were provided
vector(const vector& __x)
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:569:7: note: candidate constructor not viable: requires 1 argument, but 2 were provided
vector(vector&&) noexcept = default;
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:582:7: note: candidate constructor not viable: requires 3 arguments, but 2 were provided
vector(vector&& __rv, const allocator_type& __m, true_type) noexcept
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:586:7: note: candidate constructor not viable: requires 3 arguments, but 2 were provided
vector(vector&& __rv, const allocator_type& __m, false_type)
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:484:7: note: candidate constructor not viable: requires 0 arguments, but 2 were provided
vector() = default;
^
1 error generated.
vector<int> is not a 2D vector.
Instead of this:
a = vector<int>(16, vector<int>(15));
You should use this:
a = vector<vector<int>>(16, vector<int>(15));
I am new to C++ and was messing around with some of the things that I've learnt.
So I tried the following code:
#include <iostream>
int main() {
std::cout << std::cin;
}
So I expected the code to return an error, but instead got what I think is a memory address (0x6fccc408). Also, when running it multiple times, I got the same memory address, even after restarting cmd. What exactly does this memory address signify?
It looks like you are using C++98 or C++03. In those versions cin could be implicitly converted to a void* so what you are seeing is that conversion.
If you used C++11, which got rid of the implicit void* conversion and instead implemented a explicit conversion to bool this would produce a compiler error like
clang++ -std=c++11 -O2 -Wall -pedantic -pthread main.cpp && ./a.out
main.cpp:4:15: error: invalid operands to binary expression ('ostream' (aka 'basic_ostream<char>') and 'istream' (aka 'basic_istream<char>'))
std::cout << std::cin;
~~~~~~~~~ ^ ~~~~~~~~
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:245:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'const void *' for 1st argument; take the address of the argument with &
operator<<(const void* __p)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/system_error:209:5: note: candidate function [with _CharT = char, _Traits = std::char_traits<char>] not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'const std::error_code' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:108:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to '__ostream_type &(*)(__ostream_type &)' (aka 'basic_ostream<char, std::char_traits<char> > &(*)(basic_ostream<char, std::char_traits<char> > &)') for 1st argument
operator<<(__ostream_type& (*__pf)(__ostream_type&))
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:117:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to '__ios_type &(*)(__ios_type &)' (aka 'basic_ios<char, std::char_traits<char> > &(*)(basic_ios<char, std::char_traits<char> > &)') for 1st argument
operator<<(__ios_type& (*__pf)(__ios_type&))
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:127:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'std::ios_base &(*)(std::ios_base &)' for 1st argument
operator<<(ios_base& (*__pf) (ios_base&))
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:166:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'long' for 1st argument
operator<<(long __n)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:170:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'unsigned long' for 1st argument
operator<<(unsigned long __n)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:174:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'bool' for 1st argument
operator<<(bool __n)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:178:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'short' for 1st argument
operator<<(short __n);
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:181:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'unsigned short' for 1st argument
operator<<(unsigned short __n)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:189:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'int' for 1st argument
operator<<(int __n);
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:192:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'unsigned int' for 1st argument
operator<<(unsigned int __n)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:201:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'long long' for 1st argument
operator<<(long long __n)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:205:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'unsigned long long' for 1st argument
operator<<(unsigned long long __n)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:220:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'double' for 1st argument
operator<<(double __f)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:224:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'float' for 1st argument
operator<<(float __f)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:232:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'long double' for 1st argument
operator<<(long double __f)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:270:7: note: candidate function not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to '__streambuf_type *' (aka 'basic_streambuf<char, std::char_traits<char> > *') for 1st argument
operator<<(__streambuf_type* __sb);
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:502:5: note: candidate function [with _CharT = char, _Traits = std::char_traits<char>] not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'char' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:508:5: note: candidate function [with _Traits = std::char_traits<char>] not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'char' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __out, char __c)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:514:5: note: candidate function [with _Traits = std::char_traits<char>] not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'signed char' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:519:5: note: candidate function [with _Traits = std::char_traits<char>] not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'unsigned char' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:556:5: note: candidate function [with _Traits = std::char_traits<char>] not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'const char *' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:569:5: note: candidate function [with _Traits = std::char_traits<char>] not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'const signed char *' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:574:5: note: candidate function [with _Traits = std::char_traits<char>] not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'const unsigned char *' for 2nd argument
operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:628:5: note: candidate function [with _CharT = char, _Traits = std::char_traits<char>, _Tp = std::basic_istream<char>] not viable: no known conversion from 'ostream' (aka 'basic_ostream<char>') to 'basic_ostream<char, std::char_traits<char> > &&' for 1st argument
operator<<(basic_ostream<_CharT, _Traits>&& __os, const _Tp& __x)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/bits/ostream.tcc:321:5: note: candidate function [with _CharT = char, _Traits = std::char_traits<char>] not viable: no known conversion from 'istream' (aka 'basic_istream<char>') to 'const char *' for 2nd argument
operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:497:5: note: candidate template ignored: deduced conflicting types for parameter '_CharT' ('char' vs. 'std::basic_istream<char>')
operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/bits/basic_string.h:5325:5: note: candidate template ignored: could not match 'basic_string' against 'basic_istream'
operator<<(basic_ostream<_CharT, _Traits>& __os,
^
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/6.1.0/../../../../include/c++/6.1.0/ostream:539:5: note: candidate template ignored: could not match 'const _CharT *' against 'istream' (aka 'basic_istream<char>')
operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
^
1 error generated.
When compiling my program with clang++ --std=c++11 file.cpp the line std::unique_ptr<FILE> pipe(popen(cmd.c_str(), "r"), pclose); throws the error
memdiff.cpp:11:27: error: no matching constructor for initialization of
'std::unique_ptr<FILE>'
std::unique_ptr<FILE> pipe(popen(cmd.c_str(), "r"), pclose);
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:2530:31: note:
candidate constructor not viable: no known conversion from 'int (FILE *)'
to 'const std::__1::default_delete<__sFILE>' for 2nd argument
_LIBCPP_INLINE_VISIBILITY unique_ptr(pointer __p, typename conditional<
^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:2537:31: note:
candidate constructor not viable: no known conversion from 'int (FILE *)'
to 'typename remove_reference<deleter_type>::type' (aka
'std::__1::default_delete<__sFILE>') for 2nd argument
_LIBCPP_INLINE_VISIBILITY unique_ptr(pointer __p, typename remove_ref...
^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:2547:9: note:
candidate template ignored: could not match 'unique_ptr<type-parameter-0-0,
type-parameter-0-1>' against '__sFILE *'
unique_ptr(unique_ptr<_Up, _Ep>&& __u,
^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:2562:35: note:
candidate template ignored: could not match 'auto_ptr<type-parameter-0-0>'
against '__sFILE *'
_LIBCPP_INLINE_VISIBILITY unique_ptr(auto_ptr<_Up>&& __p,
^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:2516:49: note:
candidate constructor not viable: requires 1 argument, but 2 were provided
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR unique_ptr(nullptr_t) _NOEXCEPT
^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:2522:40: note:
candidate constructor not viable: requires single argument '__p', but 2
arguments were provided
_LIBCPP_INLINE_VISIBILITY explicit unique_ptr(pointer __p) _NOEXCEPT
^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:2543:31: note:
candidate constructor not viable: requires single argument '__u', but 2
arguments were provided
_LIBCPP_INLINE_VISIBILITY unique_ptr(unique_ptr&& __u) _NOEXCEPT
^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:2487:29: note:
candidate constructor (the implicit copy constructor) not viable: requires
1 argument, but 2 were provided
class _LIBCPP_TYPE_VIS_ONLY unique_ptr
^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:2510:49: note:
candidate constructor not viable: requires 0 arguments, but 2 were provided
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR unique_ptr() _NOEXCEPT
^
1 error generated.
If I switch from a unique_ptr to a shared_ptr my program compiles. Why does one constructor work and one not, and how do I fix it?
As correctly pointed out in the first comment: With unique_ptr, the type of the deleter must be specified as the second template parameter.
However, it's supposed to be a function pointer:
std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(cmd.c_str(), "r"), pclose);