CreateThread function

Syntax

HANDLE CreateThread(
    LPSECURITY_ATTRIBUTES   lpThreadAttributes,
    SIZE_T                  dwStackSize,
    LPTHREAD_START_ROUTINE lpStartAddress,
    __drv_aliasesMem LPVOID lpParameter,
    DWORD                   dwCreationFlags,
    LPDWORD                 lpThreadId
);

Description

The CreateThread function creates a new thread in the calling process. The new thread begins execution at the specified start address (lpStartAddress) and runs until its main function returns or calls ExitThread. The return value is a handle to the newly created thread, which can be used by other thread functions.

Parameters

Name	Type	Description
lpThreadAttributes	LPSECURITY_ATTRIBUTES	Pointer to a `SECURITY_ATTRIBUTES` structure that determines whether the returned handle can be inherited by child processes. `NULL` gives default security and non‑inheritable handle.
dwStackSize	SIZE_T	Initial thread stack size, in bytes. Zero uses the default size for the executable.
lpStartAddress	LPTHREAD_START_ROUTINE	Pointer to the application-defined function to be executed by the thread.
lpParameter	LPVOID	Pointer to a variable to be passed to `lpStartAddress`.
dwCreationFlags	DWORD	Controls the creation of the thread. Use `0` for immediate start, or `CREATE_SUSPENDED` to create it in a suspended state.
lpThreadId	LPDWORD	Pointer to a variable that receives the thread identifier. Can be `NULL`.

Return value

If the function succeeds, the return value is a handle to the new thread. If the function fails, the return value is NULL. To get extended error information, call GetLastError.

Remarks

The thread identifier returned through lpThreadId is unique only within the process; do not assume it is unique system‑wide.
Use CloseHandle when the thread handle is no longer needed.
Passing CREATE_SUSPENDED allows you to perform additional initialization before the thread runs.
Be cautious with the stack size; allocating too large of a stack can affect system resources.

Example

#include <windows.h>
#include <stdio.h>

DWORD WINAPI ThreadFunc(LPVOID lpParam) {
    int *p = (int*)lpParam;
    for (int i = 0; i < 5; ++i) {
        printf("Thread %d: %d\n", GetCurrentThreadId(), *p + i);
        Sleep(500);
    }
    return 0;
}

int main(void) {
    int value = 100;
    HANDLE hThread = CreateThread(
        NULL,               // default security attributes
        0,                  // default stack size
        ThreadFunc,         // thread function
        &value,            // parameter to thread function
        0,                  // default creation flags
        NULL);              // receive thread identifier

    if (hThread == NULL) {
        printf("CreateThread failed (%lu)\n", GetLastError());
        return 1;
    }

    WaitForSingleObject(hThread, INFINITE);
    CloseHandle(hThread);
    return 0;
}

Microsoft Docs