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CreateProcess and redirect to file using hStdOutput

allmer
allmer asked
on
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Last Modified: 2013-11-20
Hi Experts,
I would like to redirect the output of a command line program to a file using hStdOutput.
However, while the program happily displays its output in its dos window, the file is not written.
What am I doing wrong?

here is what I am doing:
      STARTUPINFO si;
      ZeroMemory( &si, sizeof(si) );
      si.cb = sizeof(si);
      si.dwFlags = STARTF_USESHOWWINDOW;
      si.wShowWindow = SW_SHOW;
      CFile file;
      file.Open(outFile.c_str(),CFile::modeWrite);
      ofstream out(outFile.c_str());

//Both approaches don't work
      si.hStdOutput = out;
                si.hStdOutput = file;
//ofstream is at least creating the file

      if( !CreateProcess(
            0,//nExeLoc.c_str(),            // Location of executable
            //Cannot take full path (spaces) MAybe with \"\"
            commandLine.GetBuffer(),// Command line parameters.
            NULL,           // Process handle not inheritable.
            NULL,           // Thread handle not inheritable.
            FALSE,          // Set handle inheritance to FALSE.
            0,              // No creation flags.
            NULL,           // Use parent's environment block.
            wd.GetBuffer(),        // Use parent's starting directory.
            &si,            // Pointer to STARTUPINFO structure.
            &procInfo )           // Pointer to PROCESS_INFORMATION structure.
      ) {
            //Error occured!
            return(false);
      }

This is urgent for me.
Thanks,
Jens
Comment
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Commented:
Instead of CFile use CreateFile function which returns HANDLE. Use this handle to fill members of STARTUPINFO structure for redirecting program output.
IT Professional
Top Expert 2005
Commented:
I think you need to specify STARTUPINFO.dwFlags = STARTF_USESTDHANDLES

As per docs :

dwFlags :
STARTF_USESTDHANDLES If this value is specified, sets the standard input of the process, standard output, and standard error handles to the handles specified in the hStdInput, hStdOutput, and hStdError members of the STARTUPINFO structure. The CreateProcess function's fInheritHandles parameter must be set to TRUE for this to work properly.

If this value is not specified, the hStdInput, hStdOutput, and hStdError members of the STARTUPINFO structure are ignored.  <==

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/base/startupinfo_str.asp


Here is full sample code :
How to spawn console processes with redirected standard handles : http://support.microsoft.com/kb/190351 <=======

-MAHESH

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mahesh1402IT Professional
Top Expert 2005

Commented:
as per bove which means you also need STARTUPINFO.bInheritHandle = TRUE

STARTUPINFO si;

si.dwFlags = STARTF_USESTDHANDLES;
si.bInheritHandle = TRUE;

...

Refer above link for full example code.

-MAHESH
jkr
CERTIFIED EXPERT
Top Expert 2012
Commented:
AlexFM is correct about 'CreateProcess()', however some constraints have to be met regarding how to set it up. Here's a code snippet (taken from 'production' code) which does that:

    SECURITY_ATTRIBUTES sa;
    STARTUPINFO         si;
    PROCESS_INFORMATION pi;
    HANDLE              hStdOut;
    BOOL                bRes;

    sa.nLength              =   sizeof  (   SECURITY_ATTRIBUTES);
    sa.lpSecurityDescriptor =   NULL;
    sa.bInheritHandle       =   TRUE;

    dwFlags =       FILE_ATTRIBUTE_NORMAL;

    hStdOut =   CreateFile  (   "c:\\test.out",
                                GENERIC_WRITE,,
                                FILE_SHARE_READ | FILE_SHARE_WRITE,
                                &sa,
                                CREATE_ALWAYS,
                                dwFlags,
                                NULL
                            );

    ZeroMemory  (   &si,    sizeof  (   STARTUPINFO));

    si.cb           =   sizeof  (   STARTUPINFO);
    si.dwFlags      =   STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES;
    si.wShowWindow  =   SW_HIDE;
    si.hStdInput    =   NULL;
    si.hStdOutput   =   hStdOut; // output file handle
    si.hStdError    =   NULL;

    bRes    =   CreateProcess   (   "sample.exe",
                                    NULL,
                                    NULL,
                                    NULL,
                                    TRUE,
                                    NORMAL_PRIORITY_CLASS,
                                    GetEnvironmentStrings   (),
                                    "C:\\somedir",
                                    &si,
                                    &pi
                                );

    // wait with patience .....
    WaitForSingleObject (   pi.hProcess,    INFINITE);
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