linux共享内存 mmap

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

int main() {
    int shm_fd;
    void *ptr;

    // 创建一个匿名共享内存对象
    shm_fd = shm_open("/my_shm", O_CREAT | O_RDWR, 0666);
    if (shm_fd == -1) {
        perror("Failed to create shared memory object");
        exit(EXIT_FAILURE);
    }

    // 调整共享内存大小
    if (ftruncate(shm_fd, sizeof(int)) == -1) {
        perror("Failed to set size of shared memory object");
        exit(EXIT_FAILURE);
    }

    // 映射共享内存到进程地址空间
    ptr = mmap(0, sizeof(int), PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
    if (ptr == MAP_FAILED) {
        perror("Failed to map shared memory");
        exit(EXIT_FAILURE);
    }

    // 写入数据到共享内存
    int *data = (int *)ptr;
    *data = 42;

    printf("Data written to shared memory: %d\n", *data);

    // 解除映射并关闭共享内存对象
    if (munmap(ptr, sizeof(int)) == -1) {
        perror("Failed to unmap shared memory");
    }
    close(shm_fd);

    return 0;
}

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

int main() {
    int shm_fd;
    void *ptr;

    // 打开已存在的共享内存对象
    shm_fd = shm_open("/my_shm", O_RDWR, 0666);
    if (shm_fd == -1) {
        perror("Failed to open shared memory object");
        exit(EXIT_FAILURE);
    }

    // 映射共享内存到进程地址空间
    ptr = mmap(0, sizeof(int), PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
    if (ptr == MAP_FAILED) {
        perror("Failed to map shared memory");
        exit(EXIT_FAILURE);
    }

    // 读取共享内存中的数据
    int *data = (int *)ptr;
    printf("Data read from shared memory: %d\n", *data);

    // 解除映射并关闭共享内存对象
    if (munmap(ptr, sizeof(int)) == -1) {
        perror("Failed to unmap shared memory");
    }
    close(shm_fd);

    return 0;
}