linux网络编程之共享内存简介和mmap函数

下面写 两个程序测试一下：

mmap_write.c

#include<string.h>
#include<stdio.h>
#include<stdlib.h>
#include<sys/ipc.h>
#include<sys/msg.h>
#include<sys/types.h>
#include<unistd.h>
#include<errno.h>
#include<fcntl.h>
#include<sys/stat.h>
#include<sys/mman.h>
    
#define ERR_EXIT(m) 
    do { 
        perror(m); 
        exit(EXIT_FAILURE); 
    } while(0)
    
typedef struct stu
{
    char name[4];
    int age;
} STU;
    
int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        fprintf(stderr, "Usage: %s <file>n", argv[0]);
        exit(EXIT_FAILURE);
    }
    
    int fd;
    fd = open(argv[1], O_CREAT | O_RDWR | O_TRUNC, 0666);
    if (fd == -1)
        ERR_EXIT("open");
    
    lseek(fd, sizeof(STU) * 5 - 1, SEEK_SET);
    write(fd, "", 1);
    
    STU *p;
    p = (STU *)mmap(NULL, sizeof(STU) * 5, PROT_READ | PROT_WRITE,
                    MAP_SHARED, fd, 0);
    
    if (p == -1)
        ERR_EXIT("mmap");
    
    char ch = 'a';
    int i;
    for (i = 0; i < 5; i++)
    {
        memcpy((p + i)->name, &ch, 1);
        (p + i)->age = 20 + i;
        ch++;
    }
    
    printf("initialize overn");
    
    munmap(p, sizeof(STU) * 5);
    printf("exit...n");
    return 0;
}

mmap_read.c

#include<string.h>
#include<stdio.h>
#include<stdlib.h>
#include<sys/ipc.h>
#include<sys/msg.h>
#include<sys/types.h>
#include<unistd.h>
#include<errno.h>
#include<fcntl.h>
#include<sys/stat.h>
#include<sys/mman.h>
    
#define ERR_EXIT(m) 
    do { 
        perror(m); 
        exit(EXIT_FAILURE); 
    } while(0)
    
typedef struct stu
{
    char name[4];
    int age;
} STU;
    
int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        fprintf(stderr, "Usage: %s <file>n", argv[0]);
        exit(EXIT_FAILURE);
    }
    
    int fd;
    fd = open(argv[1], O_RDWR);
    if (fd == -1)
        ERR_EXIT("open");
    
    
    STU *p;
    p = (STU *)mmap(NULL, sizeof(STU) * 5, PROT_READ | PROT_WRITE,
                    MAP_SHARED, fd, 0);
    
    if (p == -1)
        ERR_EXIT("mmap");
    
    int i;
    for (i = 0; i < 5; i++)
    {
        printf("name = %s age = %dn", (p + i)->name, (p + i)->age);
    }
    munmap(p, sizeof(STU) * 5);
    printf("exit...n");
    return 0;
}

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