When was the unordered_map concept built into g++?
Because the following code throws an error.
#include<iostream>
#include<unordered_map>
#include<stdio.h>
using namespace std;
std::unordered_map<std::int,int> mirror;
mirror['A'] = 'A';
mirror['B'] = '#';
mirror['E'] = 3;
int main(void)
{
std::cout<<mirror['A'];
std::cout<<mirror['B'];
std::cout<<mirror['C'];
return 0;
}
I am compiling the code as follows:
g++ -c hashexample.cpp
g++ -o result hashExample.o
./result
The error I got is this:
inavalid types int[char[ for aaray subscript
What is the fix for this?
The problem is your assignment. You cannot assign values to your map in this place. C++ is not a script language.
This program works fine on my machine with gcc4.6:
#include<iostream>
#include<unordered_map>
std::unordered_map<int,int> mirror;
int main() {
mirror['A'] = 'A';
mirror['B'] = '#';
mirror['E'] = 3;
std::cout<<mirror['A'];
std::cout<<mirror['B'];
std::cout<<mirror['C'];
}
First, as mkaes points out, you cannot put assignments outside functions, so you have to put it in any, for example main.
As for unordered_map, for recent versions of gcc, if you don't want to go into C++11, you can use the TR1 version of unordered_map:
#include <tr1/unordered_map>
and the type std::tr1::unordered_map. You know, C++11 supersedes all this, but you will (at least in GCC) get this working.
Related
This question already has an answer here:
Does clang on Mac not support uniform initialization?
(1 answer)
Closed 4 months ago.
I am trying to assign value to a vector but I keep getting different errors. I am using clang++ version 14.0.0 to build the file and I am getting the error using vs code debugger.
Here are the different erros:
When i run this code
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<int> v;
v = {0, 1};
return 0;
}
I get the error "expected expression".
When i run this code
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<int> v;
v = vector<int>{0, 1};
return 0;
}
I get error "expected '(' for function-style cast or type construction"
Neither initiliazing nor assigning the vector later seems to work.
If my problem is unclear. Please let me know how I can improve :)
clang++ on Mac defaults to using C++98 (-std=c++98) and in C++98 both errors are to be expected.
Just add
-std=c++11
(or later, like -std=c++14, -std=c++17 or -std=c++20) when compiling and both your snippets will compile fine.
Well i just wanted to do a "foreach" like statement in C++, but in reverse order. Reading a little, the doc says that adding this to the "especial" form of the for statment it can be done.
Like this:
#include <iostream>
#include <vector>
int main()
{
std::vector<int> vecInt;
for (int i = 0; i < 10; i++)
vecInt.push_back(i);
for (auto const& x : vecInt | std::views::reverse) //Here is the problem with g++ -std=c++2a
{
}
return 0;
}
The thing is that im using ubuntu linux with the latest g++ compiler.
According to what the compiler throws me. I put an "std=c++20", but it then told me: "Did you mean std=c++2a" so, i don't know what the "a" means, but i tought it would be the C++20 standard. And finally discovered that "std::views::reverse" isn't seen by the compiler.
To go to the point: i want to do a reverse "foreach" C++ statement and i can't.
Any help?
I am trying to take a string and parse it into an int. I have read the many answers out there, and it seems that using stoi is the most up-to-date way. It appears to me that stoi uses std, but I am getting Function 'stoi' could not be resolved despitre using namespace std;
#include <iostream>
#include <string>
#include <cstring>
#include <fstream>
#include<stdlib.h>
using namespace std;
int main(int argc, char* argv[]) {
string line = "";
string five = "5";
int number = stoi(five); //Error here with stoi
return 0;
}
Any ideas what is causing this?
Update:
I am using Eclipse. My flags are: -c -fmessage-length=0 -std=c++11
If you are using GCC or MINGW, then this is the answer:
std::stoi doesn't exist in g++ 4.6.1 on MinGW
This is a result of a non-standard declaration of vswprintf on
Windows. The GNU Standard Library defines
_GLIBCXX_HAVE_BROKEN_VSWPRINTF on this platform, which in turn disables the conversion functions you're attempting to use. You can
read more about this issue and macro here:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37522.
If you're willing to modify the header files distributed with MinGW,
you may be able to work around this by removing the
!defined(_GLIBCXX_HAVE_BROKEN_VSWPRINTF) macro on line 2754 of
.../lib/gcc/mingw32/4.6.1/include/c++/bits/basic_string.h, and adding
it back around lines 2905 to 2965 (the lines that reference
std::vswprintf). You won't be able to use the std::to_wstring
functions, but many of the other conversion functions should be
available.
Please always provide platform and compiler information.
Toggle on C++11 support in your compiler flags. -std=c++11 for a recent gcc. For Eclipse, please refer to the corresponding question in the FAQ and this answer explains how to get rid of the remaining Eclipse warning.
If you are amenable to parsing an int another way, how about using an STL algorithm and a C++11 lambda expression?
#include <algorithm>
#include <iostream>
#include <string>
using namespace std;
int main() {
string str = "12345";
int num = 0;
for_each(str.begin(), str.end(), [&num](char c){ num = 10 * num + (c - '0'); });
cout << str << " = " << num << endl;
}
I'm trying to compile an easy program that use the alias declaration.
This is the code:
#include <iostream>
using namespace std;
using in = int;
in main ()
{
in a = 1;
cout << a << '\n';
return 0;
}
The command I use to compile is g++ -std=c++0x program_name.cxx, using the built-in terminal in Kate on Ubuntu OS.
But it doesn't work! Any suggestion?
(instead using typedef int in; it works).
Compile in C++11 mode. Type aliasing is supported only in C++11. I suspect the g++ version that use is older and doesn't fully support c++11, hence fails with c++0x.
Compile with: g++ -std=c++11 file.cpp
and it works.
By the way, it seems to be a terrible idea to alias int in such a way.
I am trying to take a string and parse it into an int. I have read the many answers out there, and it seems that using stoi is the most up-to-date way. It appears to me that stoi uses std, but I am getting Function 'stoi' could not be resolved despitre using namespace std;
#include <iostream>
#include <string>
#include <cstring>
#include <fstream>
#include<stdlib.h>
using namespace std;
int main(int argc, char* argv[]) {
string line = "";
string five = "5";
int number = stoi(five); //Error here with stoi
return 0;
}
Any ideas what is causing this?
Update:
I am using Eclipse. My flags are: -c -fmessage-length=0 -std=c++11
If you are using GCC or MINGW, then this is the answer:
std::stoi doesn't exist in g++ 4.6.1 on MinGW
This is a result of a non-standard declaration of vswprintf on
Windows. The GNU Standard Library defines
_GLIBCXX_HAVE_BROKEN_VSWPRINTF on this platform, which in turn disables the conversion functions you're attempting to use. You can
read more about this issue and macro here:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37522.
If you're willing to modify the header files distributed with MinGW,
you may be able to work around this by removing the
!defined(_GLIBCXX_HAVE_BROKEN_VSWPRINTF) macro on line 2754 of
.../lib/gcc/mingw32/4.6.1/include/c++/bits/basic_string.h, and adding
it back around lines 2905 to 2965 (the lines that reference
std::vswprintf). You won't be able to use the std::to_wstring
functions, but many of the other conversion functions should be
available.
Please always provide platform and compiler information.
Toggle on C++11 support in your compiler flags. -std=c++11 for a recent gcc. For Eclipse, please refer to the corresponding question in the FAQ and this answer explains how to get rid of the remaining Eclipse warning.
If you are amenable to parsing an int another way, how about using an STL algorithm and a C++11 lambda expression?
#include <algorithm>
#include <iostream>
#include <string>
using namespace std;
int main() {
string str = "12345";
int num = 0;
for_each(str.begin(), str.end(), [&num](char c){ num = 10 * num + (c - '0'); });
cout << str << " = " << num << endl;
}