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Join Date: May 2008

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asianguyjtran asianguyjtran is offline

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starting program in background

May 27th, 2008

hi all
i'm new to c++ and decided to tackle c++ by doing a small project

i would like to write a program that will start other programs in the background and get its pid number

so far, i have used system() but i get the output of that program

anyone care to mentor me?

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Join Date: Oct 2007

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Duoas

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Re: starting program in background

May 27th, 2008

Link.

Check my last three posts for code.

Enjoy!

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asianguyjtran asianguyjtran is offline

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Re: starting program in background

May 27th, 2008

i just looked at that link and it appears that that is for linux.

btw. is this for windows?

does CreateProcess() work?

Last edited by asianguyjtran; May 27th, 2008 at 10:01 pm.

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Duoas

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Re: starting program in background

May 27th, 2008

I'm sorry. You said "pid" and I immediately went into *nix mode.

In Windows the terminology is that each process has a handle. Which is the same thing. Go figure.

Anyway, yes, CreateProcess() is what you want. Here's a little function to automate it a little for simple (usual) cases.

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 C++ Syntax (Toggle Plain Text) 
#include <string>
#include <windows.h>
 
HANDLE ExecProcess(
  const std::string& arg0,
  const std::string& args,
  LONGBOOL is_inherit_handles = TRUE
  ) {
  HANDLE              result = INVALID_HANDLE_VALUE;
  std::string         cmdline;
  STARTUPINFO         startup_information = {0};
  PROCESS_INFORMATION process_information = {0};
 
  startup_information.cb = sizeof( STARTUPINFO );
  cmdline = string( '\"' ) +arg0 +"\" " +args;
 
  if (CreateProcess(
    arg0.c_str(),           // full path of program to execute
    cmdline.c_str(),        // complete command line
    NULL,                   // no process attribute handle inheritance
    NULL,                   // no thread attribute handle inheritance
    is_inherit_handles,     // such as stdin, etc.
    NORMAL_PRIORITY_CLASS,  // 
    NULL,                   // use the parent's environment
    NULL,                   // use the parent's current working directory
    &startup_information,   // (all defaults)
    &process_information    // resulting process info
    ))
    result = process_information.hProcess;
 
  CloseHandle( process_information.hThread );
  return result;
  }
#include <string>
#include <windows.h>

HANDLE ExecProcess(
  const std::string& arg0,
  const std::string& args,
  LONGBOOL is_inherit_handles = TRUE
  ) {
  HANDLE              result = INVALID_HANDLE_VALUE;
  std::string         cmdline;
  STARTUPINFO         startup_information = {0};
  PROCESS_INFORMATION process_information = {0};

  startup_information.cb = sizeof( STARTUPINFO );
  cmdline = string( '\"' ) +arg0 +"\" " +args;

  if (CreateProcess(
    arg0.c_str(),           // full path of program to execute
    cmdline.c_str(),        // complete command line
    NULL,                   // no process attribute handle inheritance
    NULL,                   // no thread attribute handle inheritance
    is_inherit_handles,     // such as stdin, etc.
    NORMAL_PRIORITY_CLASS,  // 
    NULL,                   // use the parent's environment
    NULL,                   // use the parent's current working directory
    &startup_information,   // (all defaults)
    &process_information    // resulting process info
    ))
    result = process_information.hProcess;

  CloseHandle( process_information.hThread );
  return result;
  }

You can use the returned handle to obtain information about the child process and wait for specific events. For example, to wait for the child to terminate, use

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WaitForSingleObject( my_childs_process_handle, INFINITE );

Hope this helps.

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Join Date: Oct 2007

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Duoas

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Re: starting program in background

May 28th, 2008

Well good grief. Is there some sort of timeout on editing posts? I haven't been gone that long.

Anyway, to fix a couple of simple errors in the last...

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <string>
#include <windows.h>
 
HANDLE ExecProcess(
  const std::string& arg0,
  const std::string& args,
  BOOL is_inherit_handles = TRUE
  ) {
  HANDLE              result = INVALID_HANDLE_VALUE;
  std::string         cmdline;
  STARTUPINFO         startup_information = {0};
  PROCESS_INFORMATION process_information = {0};
 
  startup_information.cb = sizeof( STARTUPINFO );
  cmdline = std::string( 1, '\"' ) +arg0 +"\" " +args;
 
  if (CreateProcess(
    arg0.c_str(),           // full path of program to execute
    const_cast<char*>(
          cmdline.c_str()), // complete command line
    NULL,                   // no process attribute handle inheritance
    NULL,                   // no thread attribute handle inheritance
    is_inherit_handles,     // such as stdin, etc.
    NORMAL_PRIORITY_CLASS,  // 
    NULL,                   // use the parent's environment
    NULL,                   // use the parent's current working directory
    &startup_information,   // (all defaults)
    &process_information    // resulting process info
    ))
    result = process_information.hProcess;
 
  CloseHandle( process_information.hThread );
  return result;
  }
#include <string>
#include <windows.h>

HANDLE ExecProcess(
  const std::string& arg0,
  const std::string& args,
  BOOL is_inherit_handles = TRUE
  ) {
  HANDLE              result = INVALID_HANDLE_VALUE;
  std::string         cmdline;
  STARTUPINFO         startup_information = {0};
  PROCESS_INFORMATION process_information = {0};

  startup_information.cb = sizeof( STARTUPINFO );
  cmdline = std::string( 1, '\"' ) +arg0 +"\" " +args;

  if (CreateProcess(
    arg0.c_str(),           // full path of program to execute
    const_cast<char*>(
          cmdline.c_str()), // complete command line
    NULL,                   // no process attribute handle inheritance
    NULL,                   // no thread attribute handle inheritance
    is_inherit_handles,     // such as stdin, etc.
    NORMAL_PRIORITY_CLASS,  // 
    NULL,                   // use the parent's environment
    NULL,                   // use the parent's current working directory
    &startup_information,   // (all defaults)
    &process_information    // resulting process info
    ))
    result = process_information.hProcess;

  CloseHandle( process_information.hThread );
  return result;
  }

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asianguyjtran asianguyjtran is offline

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Re: starting program in background

May 28th, 2008

Thank you for that snippet.

I'll have to study it for a while to get the hang of things since I've been working with php for a long time now

how would you call the function, ExecProcess()?

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Duoas

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Posting Virtuoso

Re: starting program in background

May 28th, 2008

Ah, you've been brain-damaged by PHP. My condolences... er,

Oh, so you know PHP? Cool!

Call it with the full path to your program and the command line arguments exactly as you would type them at the prompt:

ExecProcess( "C:\WINDOWS\notepad.exe", "myfile.txt" );

If you don't like the idea of the new program having access to your open file descriptors, set the last argument to FALSE.

Hope this helps.

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asianguyjtran asianguyjtran is offline

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Re: starting program in background

May 28th, 2008

Do you not like php?

When I go to debug, I got the errors in my build log

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1>------ Build started: Project: VanaManager, Configuration: Debug Win32 ------
1>Compiling...
1>ExecProcess.cpp
1>c:\documents and settings\asianguyjtran\desktop\vanamanager\vanamanager\execprocess.cpp(29) : error C2664: 'CreateProcessW' : cannot convert parameter 1 from 'const char *' to 'LPCWSTR'
1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
1>VanaManager.cpp
1>c:\documents and settings\asianguyjtran\desktop\vanamanager\vanamanager\execprocess.cpp(29) : error C2664: 'CreateProcessW' : cannot convert parameter 1 from 'const char *' to 'LPCWSTR'
1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
1>Generating Code...
1>Build log was saved at "file://c:\Documents and Settings\asianguyjtran\Desktop\VanaManager\VanaManager\Debug\BuildLog.htm"
1>VanaManager - 2 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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William Hemsworth William Hemsworth is offline

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Re: starting program in background

May 29th, 2008

I think you need to disable unicode to remove those errors.
Try adding:

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#undef UNICODE

at the very beginning of your source code.

Last edited by William Hemsworth; May 29th, 2008 at 8:32 am. Reason: Solution

I need pageviews! most fun profile ever :)

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niek_e

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Re: starting program in background

#10

May 29th, 2008

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Originally Posted by williamhemswort

I think you need to disable unicode to remove those errors.
Try adding:
Help with Code Tags

C++ Syntax (Toggle Plain Text)
#undef UNICODE
#undef UNICODE
at the very beginning of your source code.

You're right, but if the OP wants to use unicode (no idea why, but: )
You could call CreateProcess like this:
CreateProcess(L"yourexe.exe", L"parameters", ....etc);

Last edited by niek_e; May 29th, 2008 at 8:35 am.