What is the equivalent to /dev/null in Windows?

I think you want NUL.

For example:

type c:autoexec.bat > NUL

doesn't create a file.

According to this message on the GCC mailing list, you can use the file "nul" instead of /dev/null:

#include <stdio.h>

int main ()
{ 
      FILE* outfile = fopen ("/dev/null", "w");
      if (outfile == NULL)
        {
      fputs ("could not open '/dev/null'", stderr);
        }
      outfile = fopen ("nul", "w");
      if (outfile == NULL)
        {
      fputs ("could not open 'nul'", stderr);
        }

      return 0;
}

(Credits to Danny for this code; copy-pasted from his message.)

You can also use this special "nul" file through redirection.

Maybe someone will get interested: here is a /dev/random and /dev/zero device drivers for Win32.