Linux之文件通信

/*
 * 后执行,尝试读取另外一个进程写入文件的内容
 */
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>

int main(void)
{
    char buf[];
    char *str = "----------test2 write secesuss--------\n";
    int ret;

    sleep();   //睡眠2秒,保证test1将数据写入test.txt文件

    int fd = open("test.txt", O_RDWR);

    //尝试读取test.txt文件中test1写入的数据
    ret = read(fd, buf, sizeof(buf));   

    //将读到的数据打印至屏幕
    write(STDOUT_FILENO, buf, ret);

    //写入数据到文件test.txth中, 未修改读写位置
    write(fd, str, strlen(str));

    printf("test2 read/write finish\n");

    close(fd);

    return ;
}

/*
 * 先执行,将数据写入文件test.txt
 */
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>

#define N 5

int main(void)
{
    char buf[];
    char *str = "--------------secesuss-------------\n";
    int ret;

    int fd = open("test.txt", O_RDWR|O_TRUNC|O_CREAT, );

    //直接打开文件写入数据
    write(fd, str, strlen(str));
    printf("test1 write into test.txt finish\n");

    sleep(N);

    lseek(fd, , SEEK_SET);
    ret = read(fd, buf, sizeof(buf));
    ret = write(STDOUT_FILENO, buf, ret);

    if (ret == -) {
        perror("write second error");
        exit();
    }

    close(fd);

    return ;
}