mmap3.c

#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/types.h>

int main(int argc, char **argv) {
    int i;
    int fd;
    int ret;
    struct stat sb;
    void *ptr;    
    char tmp[] = "hello";

    fd = open("ls.txt", O_RDWR);
    if(fd < 0) {
        printf("open() error\n");
        return -1;
    }    

    ret = fstat(fd, &sb);      
    if(ret < 0) {
        printf("fstat() error\n");
        close(fd);
        return -1;
    } 
    
    /*
        void *mmap(void *addr, size_t length, int prot, int flags,
                   int fd, off_t offset);
        int munmap(void *addr, size_t length); 
    */

    ptr = mmap(NULL, sb.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if(ptr == MAP_FAILED) {
        printf("mmap() error\n");
        close(fd);
        return -1;    
    }

    for(i=0; i<strlen(tmp); i++) {
        printf("%c", *(char *)(ptr + i));
        *(char *)(ptr + i) = tmp[i];
    }
    
    munmap(0, sb.st_size);
    return 0;
}