Mingw -- Conflicting types for function due to previous declaration

Question

To start off, I don't get this issue when I compile/"make" the code on a Linux machine which I connect to remotely. I'm experiencing it only on my Windows laptop with Mingw installed -- which I believe is causing the issue.

$ make
gcc -c parser.c
parser.c:34:7: error: conflicting types for 'gets'
   34 | char* gets(char *buf, int max)
      |       ^~~~
In file included from parser.h:4,
                 from parser.c:1:
c:\mingw\include\stdio.h:709:41: note: previous declaration of 'gets' was here
  709 | _CRTIMP __cdecl __MINGW_NOTHROW  char * gets (char *);
      |                                         ^~~~
Makefile:13: recipe for target 'parser.o' failed
make: *** [parser.o] Error 1

Here's the gets() code as requested:

char* gets(char *buf, int max)
{
  int i, cc;
  char c;

  for(i=0; i+1 < max; ){
    cc = read(0, &c, 1);
    if(cc < 1) break;
    //c = getchar();
    buf[i++] = c;
    
    if(c == '\n' || c == '\r') 
        break;
  }
  
  buf[i] = '\0';
  return buf;
}

Is there a way to fix this without changing the gets function name? Thank you sm

Answer 1

Your code works on Linux's gcc because the gets function was removed , as it should, since it was deprecated in the C99 standard and removed with C11.

For some reason the Windows MingW distribution still maintains gets and because of that you have a redefinition problem.

So unfortunately you can't use that function name, unless you remove it by hand from stdio.h , as C doesn't allow for function overloading.

Running sample on Linux gcc

Running sample on Windows gcc

Answer 2

As the error says the gets() function is already defined in stdio.h .

One trick you can do is put something like this:

#define gets MY_gets

before your definition of the gets() function.

That way you are actually defining a MY_gets() function which causes no conflict. And when you call gets() later on in your code you are actually calling MY_gets() .

If you define gets() in a header file you should include stdio.h first and then put #define gets MY_gets before the declaration of gets() in the header file.

Though I don't see why you want to refine this function if it already exists. It makes more sense to only define it if needed and surround the function with something like #ifndef HAVE_GETS and endif where HAVE_GETS should be defined based on tests done in the configure/build system.