방법1 (best)

#include <unistd.h>

if( access( fname, F_OK ) != -1 ) {
    // file exists
} else {
    // file doesn't exist
}

방법2

int exists(const char *fname)
{
    FILE *file;
    if ((file = fopen(fname, "r")))
    {
        fclose(file);
        return 1;
    }
    return 0;
}

방법3

int file_exist (char *filename)
{
  struct stat   buffer;   
  return (stat (filename, &buffer) == 0);
}

if (file_exist ("myfile.txt"))
{
  printf ("It exists\n");
}