6: Creating a Process in C

Table of Contents

• 6: Creating a Process in C

  • 6.1. Creating a Process

    • CreateProcess() Template Code

    • 6.1.1. Task

  • 6.2. Process Information

    • 6.2.1. Task

  • 6.3. Waiting for the Process to Exit

    • 6.3.1. Task

This lab shows how to create a process in Windows using the system call CreateProcess(). More information on Microsoft’s site:

• Creating Processes

• CreateProcessA function

Please create a file called lab6.c from the template C file for this assignment.

6.1. Creating a Process

Creating a process in Windows is a multi-step process:

1. Create the variables

2. Allocate memory

3. Call CreateProcess()

4. Release the process handles

CreateProcess() requires several important parameters.

1. The full path to the application or program to execute.

2. Pointer to STARTUPINFO struct.

Note

You must allocate the memory required for the struct.

1. Pointer to PROCESS_INFORMATION struct.

Here is the full parameter list for CreateProcess().

CreateProcess() Template Code

Required Include Files

#include <windows.h>

Example Usages

char exe_path[] = "C:\\Windows\\system32\\notepad.exe";
STARTUPINFO startup_info;
PROCESS_INFORMATION process_info;

BOOL process_status = FALSE;

// allocate memory and clear memory
ZeroMemory(&startup_info, sizeof(startup_info));
startup_info.cb = sizeof(startup_info);
ZeroMemory(&process_info, sizeof(process_info));

process_status = CreateProcess(
    NULL,           // Use the command line arg instead
    exe_path,       // path to exe using command line
    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
    NULL,           // Use parent's starting directory
    &startup_info,  // Pointer to STARTUPINFO structure
    &process_info); // Pointer to PROCESS_INFORMATION structure

/* Do work with handles */

// Close process handles and clean up
CloseHandle(process_info.hProcess);
CloseHandle(process_info.hThread);

6.1.1. Task

Your first task is to create a process and verify the process status.

1. Create a new process for notepad.exe.

2. Verify if that process created successfully by evaluating the return bool flag.

3. Close the process handles.

4. Print an error message with the file path and exit the program with return 1 if the process did not start.

Expected Output

// Failure
Error. Failed to execute C:\\Windows\\system64\\invalid\_file.exe.

// Success
A new Notepad opened.

6.2. Process Information

PROCESS_INFORMATION struct contains these fields:

typedef struct _PROCESS_INFORMATION {
  HANDLE hProcess;
  HANDLE hThread;
  DWORD  dwProcessId;
  DWORD  dwThreadId;
} PROCESS_INFORMATION, *PPROCESS_INFORMATION, *LPPROCESS_INFORMATION;

6.2.1. Task

1. Print the process ID of the process

Expected Output

Created a new process with ID 14156.

6.3. Waiting for the Process to Exit

At this point, your program created a new child process and then exited immediately. We can observe the behavior by using the sleep function to watch the process change parents from your program to root.

6.3.1. Task

1. Download and then start Process Explorer.

2. Use the sleep function to pause your program for 15-20 seconds.

   • Sleep(15000);

3. Find your application in the Process Explorer list. Click on the child process to highlight it.|br|

4. Watch what happens when your application exits.|br|
   

Instead of exiting or processing additional code, the parent program can use WaitForSingleObject() to wait on the child to complete its work and then terminate.

// The second field is milliseconds for a set time or INFINITE
WaitForSingleObject( process_info.hProcess, INFINITE );

5. Add function WaitForSingleObject().

6. Your program should stay active until you close the Notepad window.