在父进程和子进程之间创建管道

Question

我正在尝试在父进程和子进程之间创建一个管道。在这个管道中，子进程将写入数据，而父进程将读取并打印数据。我不知道为什么，但如果我输入一个大字符串，数据就会出错，对于包含 +- 7 个单词的字符串，它仍然可以正常工作。我猜这与缓冲区的大小有关，但无法修复它。

#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

/* in this code i will make a child process with fork command
then i will create pipe using pipe commands.
i will transfer data from the child process to the father process
omriziner code
*/

void main(int argc,char *argv[])
{
    if(argc < 2){
        printf("prototype error \n<Enter any data you wana write> \n");
        return;
    }

    int fd[2]; // creating array with 2 places for 2 fd'stdio
    // fd[0] is set to read file in the pipe
    //fd[1] is set to write file in the pipe
    int piperes;
    pid_t childpid;
    char buff[5];
    char * data = "learning to the exam";
    printf("father pid %d:\n",getpid());
    printf ("size of data is %d \n",(int)sizeof(argv[1]));
    printf ("size of buff is %d \n",(int)sizeof(buff));
    piperes = pipe(fd);
    if(piperes < 0){
        perror("PIPE ERR");
        exit(1);
    }
    printf("Pipe succeed \n");
    if((childpid = fork()) == -1){ // fork will create a child process
        perror("FORK ERR");
        exit(1);
    }
// when fork  suceed - the pid of the child will return in the parent and 0 will return in the child
// when fork fail - the pid will be -1

    printf("Fork succeed, fork return is %d and process pid is %d :\n",childpid,getpid());

    if(childpid == 0){ // if pid zero , wer in the child prcs
        close(fd[0]);    
        write(fd[1],argv[1],sizeof(argv[1])); // send data to the write fd of the pipe 
        printf("data was written to fd[1] by pid : %d \n",getpid());
        exit(0);
    }
    else{ // in this case, we're in the father process
        close(fd[1]);
        read(fd[0],buff,sizeof(argv[1])+1);
        printf("Recived data is ''%s''", buff);
        printf("By pid : %d \n",getpid());
        exit(1);
    }
}

Answer 1

sizeof(argv[1])

这并不像你想象的那样。

sizeof 在编译时计算¹，在本例中将返回 8(假设您使用的是 64 位计算机)，因为 argv[1] 是一个指针。

因为您想要字符串的长度(只能在运行时知道)，所以您应该使用:

strlen(argv[1])

<小时/>

^{1 - 在某些情况下，sizeof 在运行时进行评估。这不是其中之一。}