Blocking until process ends in Tiny Process Library

Question

I am writing C++ code that accepts a command line argument, passes it to a system command like echo and prints the response. To communicate with external process, I am using tiny-process-library. The problem with my current code is that it has to wait for a configured delay of 5 seconds.

When I tried moving my code into the Process object, I get below compilation error.

Test.cpp: In lambda function:
Test.cpp:29:3: error: ‘p_Request’ is not captured

Could somebody please help me to remove the delay and populate the Result object once the external command completes its execution?

Test.cpp

#include "process.hpp"
#include <iostream>
#include <string>

using namespace TinyProcessLib;
using namespace std;

class Request{

    public:

        string s_Request;

        bool b_requestProcessed = false;

        bool b_error = false;

        string s_Response = "No response yet";

};

void processCommand( Request* );

int main(int argc, char *argv[]){

    Request *p_Request = new Request();
    p_Request->s_Request = argv[1];
    processCommand( p_Request );
    while(!p_Request->b_requestProcessed){
    }
    cout << p_Request->s_Response << endl;
}


void processCommand( Request* p_Request ){

    if(!p_Request){
        p_Request->b_error = true;
        return;
    }
    auto output=make_shared<string>();
    Process process(string("echo ") + string(p_Request->s_Request), "", [output](const char *bytes, size_t n){
         *output+=string(bytes, n);
    });
    // Help me to remove this delay
    this_thread::sleep_for(chrono::seconds(5));
    p_Request->s_Response=*output;
    auto exit_status=process.get_exit_status();
    if(exit_status == 0){
        p_Request->b_requestProcessed = true;
        p_Request->b_error = false;
    }else{

        p_Request->b_error = true;
        p_Request->s_Response="Command Execution Failed";
    }

}

Compilation Command

g++ -std=c++11 -pthread process.cpp process_unix.cpp Test.cpp -o Test

Result with Delay

./Test  "Hello Stack Overflow"
Hello Stack Overflow

Result without Delay

./Test  "Hello Stack Overflow"
[[EMPTY_LINE]]

Answer 1

this_thread::sleep_for(chrono::seconds(5));
p_Request->s_Response=*output;
auto exit_status=process.get_exit_status();

Edit to

auto exit_status=process.get_exit_status();
p_Request->s_Response=*output;

The .get_exit_status() waits for the process to complete, and your =*output makes a copy. So in the first version you're copying an empty string (as the process hasn't finished) and the second, it's awaiting the process to complete before making the copy.