using_pipe.cpp~

// based on the example from
// https://stackoverflow.com/questions/13041416/redirect-stdout-of-two-processes-to-another-processs-stdin-in-linux-c
#include<vector>
#include<sys/types.h>
#include<sys/wait.h>
#include <unistd.h>
#include <signal.h>
#include<iostream>
#include <string.h>
/// Entry point of process A
int procA(void) {
    // Process A writing to C
    for (int i = 0; i < 30; i++)
    {
        std::cout << "Hi" << std::endl;
        usleep(5000);
    }
    std::cout << "[A] Sleeping" << std::endl;
    sleep(3);
    std::cout << "[A] Exiting" << std::endl;
    return 0;
}

/// Entry point of process B
int procB(void) {
    // Process B writing to C
    while (!std::cin.eof()) {
        // read a line of input until EOL and store in a string
        std::string line;
        std::getline(std::cin, line);
	std::cout <<"B:"<< line << std::endl;
        if (line.size () > 0)
            std::cout <<"B:"<< line << std::endl;
    }
    std::cout << "[B] saw EOF" << std::endl;
    return 0;
}

/// Entry point of process C
int procC(void) {
    // Process C reading from both A and B
    while (!std::cin.eof()) {
        // read a line of input until EOL and store in a string
        std::string line;
        std::getline(std::cin, line);
        if (line.size () > 0)
            std::cout << "[C]: " << line << std::endl;
    }
    std::cout << "[C] saw EOF" << std::endl;
    return 0;
}

int main(void)
{
    std::vector<pid_t> kids;
    // create a pipe
    int ABtoC[2];
    pipe(ABtoC);


    pid_t child_pid;
    child_pid = fork ();
    if (child_pid == 0)
    {
	  std::vector<std::string> res;
    FILE   *stream;  
    
    char   buf[1024]; 
     
    
    stream = popen( "python a1ece650.py", "r" ); //将“ls －l”命令的输出 通过管道读取（“r”参数）到FILE* stream
	char tmp[1024];
	while(fgets(tmp,sizeof(tmp),stream)!=NULL){
		if(tmp[strlen(tmp)-1]=='\n'){
			tmp[strlen(tmp)-1]='\0';		
		}	
		res.push_back(tmp);
	}
	std::cout<<res.size()<<std::endl;
   
    pclose( stream );  
       // std::cout <<"A start:"<<  std::endl;
        // start process A
        //execlp ("python", "python", "a1ece650.py", "test", (char*) NULL);
        // execl("/bin/ls", "ls", "-l", nullptr);
        //perror ("Error from arie");
        return 1;
    }
    else if (child_pid < 0) {
        std::cerr << "Error: could not fork\n";
        return 1;
    }

    kids.push_back(child_pid);
	
    child_pid = fork();
    if (child_pid == 0)
    {
        // redirect stdin from the pipe
        dup2(ABtoC[0], STDIN_FILENO);
        close(ABtoC[1]);
        close(ABtoC[0]);
	std::cout<<"c start"<<std::endl;
        // start process C
        return procC();
    }
    else if (child_pid < 0) {
        std::cerr << "Error: could not fork\n";
        return 1;
    }
sleep(10);
    kids.push_back(child_pid);
    child_pid = 0;

    // redirect stdout to the pipe
    dup2(ABtoC[1], STDOUT_FILENO);
    close(ABtoC[0]);
    close(ABtoC[1]);
	std::cout <<"B start:"<<  std::endl;
    // start process B
    int res =  procB();
std::cout <<"B end:"<<  std::endl;
    // send kill signal to all children
    for (pid_t k : kids) {
        int status;
        kill (k, SIGTERM);
        waitpid(k, &status, 0);
    }

    // exit with return code of process B
    return res;

}