C++ popen command without console

Question

when I use popen to get the output of a command, say dir, it will prompt out a console.

however, can I get the output of a command without the appearance of the console?

I am using Visual C++ and want to make an Library to return the output of some command, say, dir.

Answer 1

Assuming Windows (since this is the only platform where this behavior is endemic):

CreatePipe() to create the pipes necessary to communicate, and CreateProcess to create the child process.

HANDLE StdInHandles[2]; 
HANDLE StdOutHandles[2]; 
HANDLE StdErrHandles[2]; 

CreatePipe(&StdInHandles[0], &StdInHandles[1], NULL, 4096); 
CreatePipe(&StdOutHandles[0], &StdOutHandles[1], NULL, 4096); 
CreatePipe(&StdErrHandles[0], &StdErrHandles[1], NULL, 4096); 


STARTUPINFO si;   memset(&si, 0, sizeof(si));  /* zero out */ 

si.dwFlags =  STARTF_USESTDHANDLES; 
si.hStdInput = StdInHandles[0];  /* read handle */ 
si.hStdOutput = StdOutHandles[1];  /* write handle */
si.hStdError = StdErrHandles[1];  /* write handle */

/* fix other stuff in si */

PROCESS_INFORMATION pi; 
/* fix stuff in pi */


CreateProcess(AppName, commandline, SECURITY_ATTRIBUTES, SECURITY_ATTRIBUTES, FALSE, CREATE_NO_WINDOW |DETACHED_PROCESS, lpEnvironment, lpCurrentDirectory, &si, &pi); 

This should more than get you on your way to doing what you wish to accomplish.

Answer 2

Maybe something like this? This code will return the output but it has to wait for the process to finish.

#include <iostream>
#include <windows.h>

int runCmd(const char* cmd, std::string& outOutput) {

    HANDLE g_hChildStd_OUT_Rd = NULL;
    HANDLE g_hChildStd_OUT_Wr = NULL;
    HANDLE g_hChildStd_ERR_Rd = NULL;
    HANDLE g_hChildStd_ERR_Wr = NULL;

    SECURITY_ATTRIBUTES sa;
    // Set the bInheritHandle flag so pipe handles are inherited.
    sa.nLength = sizeof(SECURITY_ATTRIBUTES);
    sa.bInheritHandle = TRUE;
    sa.lpSecurityDescriptor = NULL;
    if (!CreatePipe(&g_hChildStd_ERR_Rd, &g_hChildStd_ERR_Wr, &sa, 0))     { return 1; } // Create a pipe for the child process's STDERR.
    if (!SetHandleInformation(g_hChildStd_ERR_Rd, HANDLE_FLAG_INHERIT, 0)) { return 1; } // Ensure the read handle to the pipe for STDERR is not inherited.
    if (!CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &sa, 0))     { return 1; } // Create a pipe for the child process's STDOUT.
    if (!SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0)) { return 1; } // Ensure the read handle to the pipe for STDOUT is not inherited

    PROCESS_INFORMATION piProcInfo;
    STARTUPINFO siStartInfo;
    bool bSuccess = FALSE;

    // Set up members of the PROCESS_INFORMATION structure.
    ZeroMemory(&piProcInfo, sizeof(PROCESS_INFORMATION));

    // Set up members of the STARTUPINFO structure.
    // This structure specifies the STDERR and STDOUT handles for redirection.
    ZeroMemory(&siStartInfo, sizeof(STARTUPINFO));
    siStartInfo.cb = sizeof(STARTUPINFO);
    siStartInfo.hStdError  = g_hChildStd_ERR_Wr;
    siStartInfo.hStdOutput = g_hChildStd_OUT_Wr;
    siStartInfo.dwFlags |= STARTF_USESTDHANDLES;

    // Create the child process.
    bSuccess = CreateProcess(
        NULL,             // program name
        (char*)cmd,       // command line
        NULL,             // process security attributes
        NULL,             // primary thread security attributes
        TRUE,             // handles are inherited
        CREATE_NO_WINDOW, // creation flags (this is what hides the window)
        NULL,             // use parent's environment
        NULL,             // use parent's current directory
        &siStartInfo,     // STARTUPINFO pointer
        &piProcInfo       // receives PROCESS_INFORMATION
    );

    CloseHandle(g_hChildStd_ERR_Wr);
    CloseHandle(g_hChildStd_OUT_Wr);

    // read output
    #define BUFSIZE 4096
    DWORD dwRead;
    CHAR chBuf[BUFSIZE];
    bool bSuccess2 = FALSE;
    for (;;) { // read stdout
        bSuccess2 = ReadFile(g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &dwRead, NULL);
        if(!bSuccess2 || dwRead == 0) break;
        std::string s(chBuf, dwRead);
        outOutput += s;
    }
    dwRead = 0;
    for (;;) { // read stderr
        bSuccess2 = ReadFile(g_hChildStd_ERR_Rd, chBuf, BUFSIZE, &dwRead, NULL);
        if(!bSuccess2 || dwRead == 0) break;
        std::string s(chBuf, dwRead);
        outOutput += s;
    }

    // The remaining open handles are cleaned up when this process terminates.
    // To avoid resource leaks in a larger application,
    // close handles explicitly.
    return 0;
}

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

    std::string output;
    runCmd("cmd /c dir", output);

    std::cout << output << std::endl;

    return 0;
}

Answer 3

With POSIX it should be something like this:

//Create the pipe.
int lsOutPipe[2];
pipe(lsOutPipe);

//Fork to two processes.
pid_t lsPid=fork();

//Check if I'm the child or parent.
if ( 0 == lsPid )
{//I'm the child.
  //Close the read end of the pipe.
  close(lsOutPipe[0]);

  //Make the pipe be my stdout.
  dup2(lsOutPipe[1],STDOUT_FILENO);

  //Replace my self with ls (using one of the exec() functions):
  exec("ls"....);//This never returns.  
} // if

//I'm the parent.
//Close the read side of the pipe.
close(lsOutPipe[1]);

//Read stuff from ls:
char buffer[1024];
int bytesRead;
do
{
  bytesRead = read(emacsInPipe[0], buffer, 1024);

  // Do something with the read information.
  if (bytesRead > 0) printf(buffer, bytesRead);
} while (bytesRead > 0);

You should off course check return values etc...