mmap.c

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

struct person {
    char name[20];
    int age;
};

static int write_info(struct person *p) {
    int fd;
    ssize_t ret;

    fd = open("list.txt", O_CREAT | O_WRONLY | O_APPEND, 0744);
    if(fd == -1) {
        printf("open() fail\n");
        return -1;
    } 

    ret = write(fd, (struct person *)p, sizeof(struct person));
    if(ret < sizeof(struct person)) {
        printf("write fail\n");
        return -1;
    }
    
    close(fd);
    return 0;
}

static int mmap_read(void) {
    int i;
    int fd;
    int ret;
    struct stat sb;
    struct person *p;

    fd = open("list.txt", O_RDONLY);
    if(fd == -1) {
        printf("open() fail\n");
        return -1;
    }
    
    /*
    
    void *mmap(void *addr, size_t length, int prot, int flags,
            int fd, off_t offset);

    int fstat(int fd, struct stat *buf);

    */

    ret = fstat(fd, &sb);
    if(ret == -1) {
        printf("fstat() error\n");
        close(fd);
        return -1;
    }

    p = mmap(0, sb.st_size, PROT_READ, MAP_SHARED, fd, 0);
    if(p == MAP_FAILED) {
        printf("mmap() fail\n");
        close(fd);
        return -1;
    }      

    for(i=0; i<sb.st_size/sizeof(struct person); i++) {
        printf("name : %s, age = %d\n", 
                p[i].name, p[i].age);
    }
    
    close(fd);
    return 0;
}

int main(int argc, char **argv) {
    struct person p[2] = { { "유영재", 20}, {"손님", 30} };
    write_info(&p[0]);
    write_info(&p[1]);
    
    mmap_read();
    return 0;
}