execlp（）输出无法使用管道重定向到stdout

Question

I have the following program:

#include<iostream>
#include<fcntl.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<unistd.h>

using namespace std;

int main()
{
  int p[2];
  int code;
  pid_t pid;
  if(-1==(pipe(p)))
  {
    cout<<"Pipe error!"<<endl;
    return 1;
  }
  if(-1==(pid=fork()))
  {
    cout<<"Fork error!"<<endl;
    return 1;
  }
  if(pid==0)
  {
     dup2(p[1],1);//duplicates stdout?
     close(p[0]);//closes reading end
     execlp("grep","grep","/bin/bash","/etc/passwd",NULL);
     return 1;
  }
  else
  {
    cout<<"works so far"<<endl;
    wait(&code);
    cout<<"Doesn't get here"<<endl;
    //how do i read from the pipe to print on the screen what execlp wanted to ?
  }
return 1;
}

I want to redirect the execlp output in the pipe so that the parent can read it and print it itself. I understand that execlp overwrites the child process and it prints to stdout itself, but i need the parent to do that.

From what i understand so far, when i do dup2(p[1],1) it duplicates the stdout and it closes it too. So that execlp would write to the lowest value descriptor (that being my pipe since it closed and copied stdout). Where am i wrong ?

ps I compile with g++

Answer 1

我设法通过将stdout指向文件（描述符）来解决此问题，然后在父进程中打开并从中读取execlp的输出。