Error "'fdopen' was not declared" found with g++ 4 that compiled with g++3
c++, g++-4.7
Solution
The problem comes from `-std=c++11`. The `fdopen()` function is not in ANSI C (only in the POSIX standard), and compiling with `-std=c++11` option implies defining `__STRICT_ANSI__`, which excludes several functions from `stdio.h`. By the way, in C++ programs, you should normally include `<cstdio>` instead of `<stdio.h>`, see here: stdio.h not standard in C++?.
If you need to use `fdopen()`, you might want to remove the `-std=c++11` option when compiling. Another possible soltion, although not really elegant, can be to use this in your source code:
#ifdef __STRICT_ANSI__
#undef __STRICT_ANSI__
#include <cstdio>
#define __STRICT_ANSI__
#else
#include <cstdio>
#endif
(which is intended to work with and without the `-std=c++11` option).
Problem
I have code that compiled happily with g++ version 3.something. I then wanted to build some other code that had C++11 symbols in it so I upgraded to g++ 4.7. Now my original code doesn't build. I get the error: 'fdopen' was not declared in this scope According to the man page, fdopen() is declared in stdio.h which I am including. I'm not sure it is relevant, but I am working in a Cygwin environment. The exact version of g++ I am using is version 4.7.2 provided by Cygwin. I have not changed this code since I switched compiler and I can definitely confirm that it built and my test code ran and passed with the previous compiler. As requested, example code to demonstrate the problem: ``` #include <stdio.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> int main(int argc, char **argv) { int fd; FILE *fp; fd = open("test.txt", (O_WRONLY | O_CREAT | O_EXCL), S_IRWXU); if(0 < fd) { fp = fdopen(fd, "wb"); fprintf(fp, "Testing...\n"); fclose(fp); } return 0; } # g++ -std=c++11 -o test test.cpp test.cpp: In function 'int main(int, char**)': test.cpp:14:29: error: 'fdopen' was not declared in this scope ```