CreateProcess and CreatePipe to execute a process and return output as a string in VC++

Question

I am trying to use CreateProcess and CreatePipe to execute a process from within a Windows Forms C++/CLR application in Visual Studio 2010.

Answer 1

Thanks to Hans Passant for the lead that got me to this clear and simple piece of code that does exactly what I was looking for.

/// this namespace call is necessary for the rest of the code to work
using namespace System::Diagnostics;
using namespace System::Text;/// added for encoding

Process^ myprocess = gcnew Process;
Encoding^ Encoding;/// added for encoding
Encoding->GetEncoding(GetOEMCP());/// added for encoding

myprocess->StartInfo->FileName = "ping.exe";
myprocess->StartInfo->Arguments = "127.0.0.1";
myprocess->StartInfo->UseShellExecute = false;

/// added the next line to keep a new window from opening
myprocess->StartInfo->CreateNoWindow = true;

myprocess->StartInfo->RedirectStandardOutput = true;
myprocess->StartInfo->StandardOutputEncoding = Encoding;/// added for encoding
myprocess->Start();

String^ output = gcnew String( myprocess->StandardOutput->ReadToEnd() );

myprocess->WaitForExit();

/// OutputBox is the name of a Windows Forms text box in my app.
OutputBox->Text = output;

EDIT: Added encoding information. See above code.

Answer 2

You are not making correct use of the ::ReadFile() function.

Read about it here: http://msdn.microsoft.com/en-us/library/ms891445.aspx

Basically, you want to fail with an error if the function ever does not return TRUE, and you want to keep looping until it yields a zero reDword.

Also, ::ReadFile() will not zero-terminate your data for you, so you have to do it yourself, like this: buf[reDword] = '\0'; (make sure your buf is 101 chars long before doing that.)

EDIT: Since I was asked to provide some example code, here it is, though I have not gone through the trouble of actually compiling it to make sure it works, so please beware of syntax errors, and generally consider it only as a rough pointer to the direction in which it should be done:

#define BUFFER_SIZE 100
string csoutput;
for( ;; )
{
    char buf[BUFFER_SIZE+1];
    DWORD redword; 
    if( !::ReadFile(rPipe,buf,BUFFER_SIZE,&redword,0) )
    {
        DWORD error = ::GetLastError();
        //throw new Exception( "Error " + error ); //or something similar
    }
    if( redword == 0 )
        break;
    buf[redword] = '\0';
    string cstemp = buf;
    csoutput += cstemp;
}
return csoutput;