source: bootcd/isolinux/syslinux-6.03/com32/lib/fopen.c

/*
 * fopen.c
 */

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

FILE *fopen(const char *file, const char *mode)
{
    int flags = O_RDONLY;
    int plus = 0;
    int fd;

    while (*mode) {
        switch (*mode) {
        case 'r':
            flags = O_RDONLY;
            break;
        case 'w':
            flags = O_WRONLY | O_CREAT | O_TRUNC;
            break;
        case 'a':
            flags = O_WRONLY | O_CREAT | O_APPEND;
            break;
        case '+':
            plus = 1;
            break;
        }
        mode++;
    }

    if (plus) {
        flags = (flags & ~(O_RDONLY | O_WRONLY)) | O_RDWR;
    }

    fd = open(file, flags, 0666);

    if (fd < 0)
        return NULL;
    else
        return fdopen(fd, mode);
}