前叉，管道执行器和dub2 [英] fork, pipe exec and dub2

问题描述

该代码应该打印"ls -l'的输出:"并附加结果"ls -l"，但不会... 有人知道这是怎么回事吗?

This code is supposed to print "Output from 'ls -l':" and append the result of 'ls -l', but it doesn't... Does anyone has a clue whats wrong with this?

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

void readStringFromFile (int file, char * readbuffer) {
    int nbytes = read(file, readbuffer, sizeof(readbuffer));
    readbuffer[nbytes] = 0;
}

int main(int argc, char const *argv[])
{
    int fd[2];
    pipe(fd);

    if (fork()==0)//child process
    {   
        close(fd[0]);
        dup2(fd[1],1);
        int retValue = execl("/bin/ls","ls","-l", NULL);
        printf("Exec failed: retValue = %d\n",retValue);
    } else
    {
        int status;
        close(fd[1]);
        wait(&status);
        char readbuffer[1024];
        readStringFromFile(fd[0],readbuffer);
        printf("Output from 'ls -l':\n %s", readbuffer);
    }
}

推荐答案

在您的代码中，以下代码段中的sizeof(readbuffer)等于4，因此它最多读取4个字节.

In your code the sizeof(readbuffer) is equal to 4 in the following snippet., so it reads 4 bytes max.

void readStringFromFile (int file, char * readbuffer) {
   int nbytes = read(file, readbuffer, sizeof(readbuffer));
   readbuffer[nbytes] = 0;
}

您可以将缓冲区的大小作为另一个参数发送，给出:

You can send the size of the buffer as another parameter, giving:

void readStringFromFile (int file, char * readbuffer, int maxsize) {
   int nbytes = read(file, readbuffer, maxsize);
   readbuffer[nbytes] = 0;
}

并使用以下命令调用它:

and invoke it with:

readStringFromFile(fd[0], readbuffer, sizeof(readbuffer));

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