pipes.cpp

#include <Windows.h>
#include <iostream>
#include <thread>

struct pipe
{
    pipe()
    {
        SECURITY_ATTRIBUTES sa = { sizeof(sa), nullptr,true};
        CreatePipe(&read, &write, &sa, 0);
    }

    ~pipe()
    {
        if(read)  CloseHandle(read);
        if(write) CloseHandle(write);
    }

    void closeRead()
    {
        CloseHandle(read);
        read=nullptr;
    }

    void closeWrite()
    {
        CloseHandle(write);
        write=nullptr;
    }

    HANDLE read {nullptr};
    HANDLE write{nullptr};
};


struct processInfo : public PROCESS_INFORMATION
{
    processInfo() : PROCESS_INFORMATION{}
    {
    }

    ~processInfo()
    {
        if(hProcess) CloseHandle(hProcess);
        if(hThread)  CloseHandle(hThread);
    }
};


struct startupInfo : public STARTUPINFO
{
    startupInfo() : STARTUPINFO{sizeof STARTUPINFO}
    {}
};



void reader(HANDLE stdout_pipe)
{
    DWORD br;
    char output[256]{};

    while(ReadFile(stdout_pipe, output, 255, &br, nullptr))
    {
        output[br]='\0';
        std::cout << output;
    }
}


int main(void)
{
    pipe stdinPipe;
    pipe stdoutPipe;
    pipe stderrPipe;

    std::thread stdoutReader{::reader,stdoutPipe.read};      // read from the read end of the stdout pipe
    std::thread stderrReader{::reader,stderrPipe.read};

    char cmdline[] = R"(findstr /i hello c:\temp\*.txt)";

    processInfo pi;
    startupInfo si;

    si.dwFlags    = STARTF_USESTDHANDLES;
    si.hStdInput  = stdinPipe.read;
    si.hStdOutput = stdoutPipe.write;                        // give the the write end of the stdout pipe to the child so it can write to it.
    si.hStdError  = stderrPipe.write;

                          
    CreateProcess(nullptr, cmdline, nullptr, nullptr, true, 0, nullptr, nullptr, &si, &pi);

    // new process has now inherited these handles.  Close our copy, so we can detect when the child closes their copy.
    stdinPipe.closeRead();
    stdoutPipe.closeWrite();
    stderrPipe.closeWrite();

    stdoutReader.join();
    stderrReader.join();
}