How do I fix “‘struct _IO_FILE’ has no member named ‘_file'”?

I have a version of a program that used to compile to a *.o file, but now it does not, and gives a compiler error.

I have tried to compile my code with gcc compiler on Linux, and the compile fails.

#include <stdio.h>
int isatty();

long isatty_(lio_number)
long *lio_number;
{
        int file_desc;

        if ((*lio_number)==5)
        {
                file_desc = stdin->_file;
                return isatty(file_desc);
        }
        else
                return 0;
}

I expect the command gcc -c isatty.c to yield isatty.o but it does not. Instead, I get this message:

isatty.c: In function ‘isatty_’:
isatty.c:11: error: ‘struct _IO_FILE’ has no member named ‘_file’

Answer

Never use any members of the FILE structure.

Use fileno(stdin) instead of stdin->_file.

The member _file is a MinGW-specific name for the file descriptor, while fileno is a widely-supported POSIX-compliant function.

Along with that, you may want to #include <unistd.h> instead of defining isatty explicitly.

If you’re limited to writing your code this way for some reason, don’t expect it to be portable. Otherwise, this should work:

#include <stdio.h>
#include <unistd.h>

long isatty_(long *lio_number)
{
        int file_desc;

        if (*lio_number == 5)
        {
                file_desc = fileno(stdin);
                return isatty(file_desc);
        }
        else
        {
                return 0;
        }
}

What this changes is that it includes unistd.h which provides a declaration for isatty, it includes the types of the arguments within the function definition, and it uses fileno(stdin) instead of stdin->_file, of which the former is much more portable. It also improves the formatting so others can read your code if they need to.