Win32 Process & Thread API

Overview

The Win32 API provides a rich set of functions for creating and managing processes and threads. This page covers the most commonly used functions, best‑practice patterns, and live code examples.

Create a Process

Use CreateProcess for full control over the new process. Below is a minimal example in C++.

C++

Explanation

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

int main() {
    STARTUPINFO si = { sizeof(si) };
    PROCESS_INFORMATION pi;

    // Command line to execute
    const wchar_t* cmd = L"notepad.exe";

    BOOL ok = CreateProcessW(
        nullptr,               // Application name
        (LPWSTR)cmd,           // Command line
        nullptr, nullptr,     // Process & thread security
        FALSE,                // Inherit handles?
        0,                     // Creation flags
        nullptr, nullptr,     // Environment & starting directory
        &si, &pi);

    if (!ok) {
        std::wcerr << L"CreateProcess failed: " << GetLastError() << std::endl;
        return 1;
    }

    std::wcout << L"Process started with PID " << pi.dwProcessId << std::endl;

    // Wait for the process to exit
    WaitForSingleObject(pi.hProcess, INFINITE);

    CloseHandle(pi.hThread);
    CloseHandle(pi.hProcess);
    return 0;
}

Key points:

STARTUPINFO controls window appearance and handles.
PROCESS_INFORMATION receives process and thread handles/IDs.
Always close the handles when you’re done to avoid leaks.
Check GetLastError for detailed failure reasons.

Create a Thread

Use CreateThread or _beginthreadex for C/C++ programs. Here’s a simple example that prints numbers.

C++

Explanation

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

DWORD WINAPI Counter(LPVOID param) {
    int limit = *(int*)param;
    for (int i = 1; i <= limit; ++i) {
        std::cout << "Thread: " << i << std::endl;
        Sleep(200);
    }
    return 0;
}

int main() {
    int count = 10;
    HANDLE hThread = CreateThread(
        nullptr,               // default security
        0,                     // default stack size
        Counter,               // thread function
        &count,               // parameter
        0,                     // run immediately
        nullptr);              // thread identifier

    if (!hThread) {
        std::cerr << "CreateThread failed: " << GetLastError() << std::endl;
        return 1;
    }

    std::cout << "Main thread continues..." << std::endl;
    WaitForSingleObject(hThread, INFINITE);
    CloseHandle(hThread);
    return 0;
}

Tips:

Pass a pointer to data you need inside the thread (must remain valid).
Always join with WaitForSingleObject or close the handle if you don’t need to wait.
For C++11 and later, consider std::thread which wraps the Win32 API.

Common Functions

Function	Purpose	Header
CreateProcess	Create a new process with full control.	windows.h
CreateThread	Start a new thread in the current process.	windows.h
ExitProcess	Terminate the current process.	windows.h
TerminateThread	Forcefully end a thread (use with care).	windows.h
WaitForSingleObject	Wait for a handle (process/thread) to become signaled.	windows.h