I just (re)installed MinGW from scratch, with gcc 4.8.1 (the latest available), and the following program won't compile:
#include <iostream>
#include <string>
int main()
{
float f;
std::string s = "5.235";
f = std::stof(s);
std::cout << f << '\n';
}
Here's the command I use:
g++ -std=c++11 -o test test.cpp
I get this error:
test.cpp:8:9: error: 'stof' is not a member of 'std'
f = std::stof(s);
^
The file bits\basic_string.h which declares std::stof is included properly in the string header, and I checked bits\basic_string.h for std::stof's declaration, and it's there.
After a bit of Googling I did find some old patches for MinGW (4.6 - 4.7) but they seem irrelevant since I'm on gcc 4.8.
Any ideas? Thanks in advance.
Not sure about exact problem, but check mingw-w64 they have gcc 4.9.2 for now. It compiles your code just well. (But since the mingw-w64 project on sourceforge.net is moving to mingw-w64.org it's better to use mingw-w64.org)
Despite of it's name it provides compilers for both x86 and x64 targets.
Probably this should be a comment, not an answer.
Related
The date library is very useful but you can see a lot of warnings after compiling a simple example that uses date library.
for example:
#include "date.h"
int main() {
using namespace date;
std::cout << weekday{July/4/2001} << '\n';
}
compiled with:
g++ -c -Waggregate-return main.cpp
warning: function call has aggregate value [-Waggregate-return]...
Depending on the version of your compiler, C++11 (or later) mode might not be active, so try adding -std=gnu++0x at least. Also you code needs #include <iostream> added.
To fix these warnings you should remove the flag -Waggregate-return from your compile string. This flag causes warnings for valid code.
Note that you also need #include <iostream>, and for older versions of g++ , -std=c++14 or a similar flag.
I seem to have written some code that works as intended on OSX (Sierra) and Debian (stable), with various versions of clang++, but doesn't want to compile on Mint (Cinnamon) with the very same versions of clang++.
To the best of my knowledge, this snippet of code is valid C++14 (and was condensed from a larger bit of code I'm working on):
#include <iostream>
#include <map>
#include <vector>
using frobs = std::map<int, int>;
struct sampleData {
frobs in;
int out;
};
int main(void) {
std::vector<sampleData> tests{
{{}, 0},
{{{1, 2}}, 3},
};
for (const auto &tt : tests) {
for (const auto &t : tt.in) {
std::cout << t.first << "\n";
}
}
return 0;
}
And compiling this on Debian with clang++ 3.5 like this:
clang++ -std=c++14 -stdlib=libc++ initialiser.cpp -o initialiser
... works and does not complain. However, on Mint Cinnamon with the same clang++ version:
clang++-3.5 -std=c++14 -stdlib=libc++ initialiser.cpp -o initialiser
Complains thusly:
initialiser.cpp:14:27: error: no matching constructor for initialization of 'std::vector<sampleData>'
std::vector<sampleData> tests{
See: http://paste.ubuntu.com/24494631/ for the full error.
I'm quite confused, especially since this seems to work fine on OSX with the clang++ bundled by Xcode as well. I've also installed libc++1 and libc++-dev on both Mint and Debian, and the problem persists if I update to newer versions of clang++ on Mint, while working correctly on Debian.
Note that in this case the weird part is that the same version of clang++ disagree, and I don't care if this compiles and works with G++ (although it does, on all the systems involved, if I use -std=c++11 and omit -stdlib=libc++ which doesn't seem supported by G++).
So, I suppose the questions are:
is this bit of code legal in the first place?
is this an issue with Mint in some way?
how do I get this to work on Mint? Do I need to install additional packages or modify the code?
My code:
#include <iostream>
#include <string>
int main()
{
std::string test = "45";
int myint = std::stoi(test);
std::cout << myint << '\n';
}
Gives me the compile error:
error: 'stoi' is not a member of 'std'
int myint = std::stoi(test);
^
However, according to here, this code should compile fine. I am using the line set(CMAKE_CXX_FLAGS "-std=c++11 -O3") in my CMakeLists.txt file.
Why is it not compiling?
Update: I am using gcc, and running gcc --version prints out:
gcc (Ubuntu 5.2.1-22ubuntu2) 5.2.1 20151010
In libstdc++, the definitions of stoi, stol, etc., as well as the to_string functions, are guarded by the condition
#if ((__cplusplus >= 201103L) && defined(_GLIBCXX_USE_C99) \
&& !defined(_GLIBCXX_HAVE_BROKEN_VSWPRINTF))
I have had this fail on one platform before (namely Termux on Android), resulting in to_string not being available even with g++ 6.1 and the C++14 standard. In that case, I just did
#define _GLIBCXX_USE_C99 1
before including anything, and voilà, suddenly the functions existed. (You should put this first, or even on the command line, rather than just before including <string>, because another header may include <string> first, and then its include guards will keep it from ever seeing your macro.)
I did not investigate why this macro wasn't set in the first place. Obviously this is a cause for concern if you want your code to actually work (in my case I didn't particularly, but FWIW there were no problems.)
You should check if _GLIBCXX_USE_C99 is not defined, or if _GLIBCXX_HAVE_BROKEN_VSWPRINTF is defined (which may be the case on MinGW?)
std::stoi is a C++11 function. You have to use the -std=c++11 to enable it in both g++ and clang++. This is the actual issue, not a linking error or a specific preprocessor define.
$ cat test.cxx
#include <iostream>
#include <string>
int main()
{
std::string test = "45";
int myint = std::stoi(test);
std::cout << myint << '\n';
}
$ g++ -otest test.cxx
test.cxx: In Funktion »int main()«:
test.cxx:7:17: Fehler: »stoi« ist kein Element von »std«
int myint = std::stoi(test);
^
$ g++ -otest test.cxx -std=c++11
$ ./test
45
$
edit: I just saw that you used c++11. Are you sure that's making it into your compile options? Check the generated makefile and watch the executed commands to be certain.
Your version seems up to date, so there shouldn't be an issue. I think it may be related to gcc. Try g++ instead.(Most likely automatically linking issue. If you just run gcc on a C++ file, it will not 'just work' like g++ does. That's because it won't automatically link to the C++ std library, etc.). My second advise is try std::atoi.
# I have fixed the issue. std::stoi uses libstdc++. It is about The GNU Standard C++ Library. In gcc you have to link adding -lstdc++. However, in g++, libstdc++ is linked automatically.
using gcc and using g++
Pay attention how it is compiled
using g++: g++ -std=c++11 -O3 -Wall -pedantic main.cpp && ./a.out
using gcc: gcc -std=c++11 -O3 -Wall -pedantic -lstdc++ main.cpp && ./a.out
I think you should set flag like set(CMAKE_EXE_LINKER_FLAGS "-libgcc -lstdc++") (Not tested)
#include <cstdlib>
int myInt = std::atoi(test.c_str());
If you are using Cmake to compile, add line:
"add_definitions(-std=c++11)"
after find_package command.
Use 'set(CMAKE_CXX_STANDARD 11)' for Cmake
When I run following code snippet from Xcode4.6 it compiles and runs fine. But when I try to compile it using command line tool (clang++) it fails to do so.
#include <iostream>
#include <memory>
int main(int argc, const char * argv[])
{
std::unique_ptr<int> foo(new int(0));
// insert code here...
std::cout << "Hello, this is cool giri World!\n";
return 0;
}
Here is compile log:
$ clang --version
Apple LLVM version 4.2 (clang-425.0.24) (based on LLVM 3.2svn)
Target: x86_64-apple-darwin12.2.0
Thread model: posix
$ clang++ main.cpp -stdlib=libc++ -I /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk/usr/include/c++/4.2.1/ -I /usr/llvm-gcc-4.2/lib/gcc/i686-apple-darwin11/4.2.1/include/
main.cpp:7:10: error: no member named 'unique_ptr' in namespace 'std'
std::unique_ptr foo(new int(0));
~~~~~^
main.cpp:7:24: error: expected '(' for function-style cast or type construction
std::unique_ptr foo(new int(0));
~~~^
main.cpp:7:26: error: use of undeclared identifier 'foo'
std::unique_ptr foo(new int(0));
^
3 errors generated.
Try using clang's own standard library:
clang -std=c++11 -stdlib=libc++ main.cpp
The default is GNU's standard library (libstdc++), but the version Apple included is quite old and doesn't have C++11 support.
You can look for yourself to see what command line Xcode used.
Build your project in Xcode.
Switch to log view. The icon for it looks like a speech bubble with a couple of lines in it.
Click on the latest build.
A list of build steps will show up in the main editing area. Right-click on "Compile main.cpp" and select "Copy Transcript for Shown Results".
Paste this into your favorite text editor to see the exact command line that Xcode used to build your project.
Make sure you are invoking clang++, not clang, for both the compiler and linker.
clang++ (as compiler) needs the -std=c++11 and -stdlib=libc++ compiler flags, and clang++ (as linker) needs the -stdlib=libc++ linker flag.
thanks Everyone for suggesting me solutions which kept me going.
Finally this is what worked for me.
I uninstalled command line tools using shell script mentioned in http://www.cocoanetics.com/2012/07/you-dont-need-the-xcode-command-line-tools/
and then used
$xcode-select -switch /Applications/Xcode.app/Contents/Developer/
to set xcode version . and finally used
$xcrun clang++ main1.cpp -stdlib=libc++
to compile my code.
This worked fine. thanks!!
I got some quite strange errors compiling code under gcc. It tells me that std::function does not exist.
I can recreate the error with the following code:
#include <functional>
#include <stdio.h>
void test(){ printf ("test"); }
int main() {
std::function<void()> f;
f = test;
f();
}
If I run gcc (from cygwin): (my error message was German, so i translated it. It may be sound different on a English gcc)
$ gcc test.cpp
test.cpp: in function "int main():
test.cpp:7:3: Error: "function" is not an element of "std"«
test.cpp:7:25: Error: "f" was not defined in this scope
With MSVC it compiled successfully.
Please tell me what I am doing wrong in my code.
Johannes
Compile it as:
g++ test.cpp -std=c++0x
-std=c++0x is needed because you're using C++11 features, otherwise g++ test.cpp is enough.
Make sure you've latest version of GCC. You can check the version as:
g++ --version
You need to compile in C++ mode, and in C++11 mode. So you need g++ and the -std flag set to c++0x.
g++ test.cpp -std=c++0x
You can also use -std=c++11 from gcc 4.7 onwards.