问C++管道错误，永远处于pipe_wait状态

EN

#include <iostream>
#include <string>
#include <sys/wait.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <vector>
#include <sstream>
#include <stdio.h>
using namespace std;

int main() {

    int pipe_A[2];
    int pipe_B[2];

    pipe(pipe_A);
    pipe(pipe_B);

    pid_t pid_A, pid_B, pid_C;

    if (!(pid_A = fork())) {
        dup2(pipe_A[1], 1); /* redirect standard output to pipe_A write end */

        system("./data");
        exit(0);
    }

    if (!(pid_B = fork())) {
        dup2(pipe_A[0], 0); /* redirect standard input to pipe_A read end */
        dup2(pipe_B[1], 1); /* redirect standard output to pipe_B write end */

        system("grep 5");
        exit(0);
    }

    if (!(pid_C = fork())) {
        dup2(pipe_B[0], 0); /* redirect standard input to pipe_B read end */

        system("grep 2");
        exit(0);
    }

    return 0;
}

for(int i=0;i<100;i++){
cout<<i<<endl;
}