posix_sem_write.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
 
#define MAXSIZE 1024*4   /*共享内存的大小，建议设置成内存页的整数倍*/
#define FILENAME "shm.test"
 
int main(int argc,int *argv[])
{
    /* 创建共享对象,可以查看/dev/shm目录 */
    int fd = shm_open(FILENAME, O_CREAT | O_TRUNC | O_RDWR, 0777);
    if (fd == -1) {
        perror("open failed:");
        exit(1);
    }
 
    /* 调整大小 */
    if (ftruncate(fd, MAXSIZE) == -1) {
        perror("ftruncate failed:");
        exit(1);
    }
 
    /* 获取属性 */
    struct stat buf;
    if (fstat(fd, &buf) == -1) {
        perror("fstat failed:");
        exit(1);
    }
    printf("the shm object size is %ld\n", buf.st_size);
 
    /* 建立映射关系 */
    char *ptr = (char*)mmap(NULL, MAXSIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (ptr == MAP_FAILED) {
        perror("mmap failed:");
        exit(1);
    }
    printf("mmap %s success\n", FILENAME);
    close(fd); /* 关闭套接字 */
 
    /* 写入数据 */
    char buf1[1024] = {0};
    printf("pls input the words....\n");
    fgets(buf1,sizeof(buf1)-1,stdin);
    strncpy(ptr, buf1, strlen(buf1));
 
    sleep(30);
 
    return 0;
}

posix_sem_read.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
 
#define FILENAME "shm.test"
 
int main()
{
    /* 创建共享对象,可以查看/dev/shm目录 */
    int fd = shm_open(FILENAME, O_RDONLY, 0);
    if (fd == -1) {
        perror("open failed:");
        exit(1);
    }
 
    /* 获取属性 */
    struct stat buf;
    if (fstat(fd, &buf) == -1) {
        perror("fstat failed:");
        exit(1);
    }
    printf("the shm object size is %ld\n", buf.st_size);
 
    /* 建立映射关系 */
    char *ptr = (char*)mmap(NULL, buf.st_size, PROT_READ, MAP_SHARED, fd, 0);
    if (ptr == MAP_FAILED) {
        perror("mmap failed:");
        exit(1);
    }
    printf("mmap %s success\n", FILENAME);
    close(fd); /* 关闭套接字 */
 
    printf("the read msg is:%s\n", ptr);
 
    sleep(30);
 
    return 0;
}

执行完write程序后，会在/dev/shm目录下生成一个shm.test

可以通过cat shm.test ，会输出对应的存储内容