CreateThread 中的转换错误

Question

当我尝试使用CreateThread函数时，我遇到了一个奇怪的错误。这是我的代码:

HANDLE threads[3];  //threads[0] is printer, threads[1] is receiver, [2] is serverconn
    DWORD  printer_id,  receiver_id, serverconn_id;
    if(
                      ((threads [0] = CreateThread(NULL, 0, printer_thread,    (LPVOID) thread_args, 0, &printer_id)) == NULL) ||
        ((recv_thread = threads [1] = CreateThread(NULL, 0, receiver_thread,   (LPVOID) thread_args, 0, &receiver_id)) == NULL) ||
                      ((threads [2] = CreateThread(NULL, 0, serverconn_thread, (LPVOID) thread_args, 0, &serverconn_id)) == NULL)
    )
    {
        IO_print_line("Initialization error");
        return FALSE;
    }

printer_thread、receiver_thread 和 serverconn_thread 的函数定义如下:

int serverconn_thread(LPVOID args);

Visual Studio 编译器给我这个错误:

Error   C2440   'function': cannot convert from 'int (__cdecl *)(LPVOID)' to 'LPTHREAD_START_ROUTINE'

我真的不明白，因为我认为我已经完全做到了 what the official documentation suggests 。

不，将线程函数的返回类型更改为 DWORD 并不能解决任何问题，错误只会更改为:

Error   C2440   'function': cannot convert from 'DWORD (__cdecl *)(LPVOID)' to 'LPTHREAD_START_ROUTINE'

奇怪的是，如果我像这样改变它:

if(
                      ((threads [0] = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE) &printer_thread,    (LPVOID) thread_args, 0, &printer_id)) == NULL) ||
        ((recv_thread = threads [1] = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE) &receiver_thread,   (LPVOID) thread_args, 0, &receiver_id)) == NULL) ||
                      ((threads [2] = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE) &serverconn_thread, (LPVOID) thread_args, 0, &serverconn_id)) == NULL)
    )

通过强制转换，编译器没问题，但我认为以这种方式强制转换不是一个好主意。我该如何解决这个问题？

Answer 1

您没有关注official documentation当声明你的线程函数时。

您的原始声明使用 int 作为返回值，并使用 __cdecl (隐式)作为调用约定。当您将返回值更改为DWORD时，您没有更改调用约定。

但是，documentation清楚地显示了正确的声明:

DWORD WINAPI ThreadProc(  _In_ LPVOID lpParameter);

DWORD is an unsigned long, and WINAPI is a macro that maps to the __stdcall calling convention (see Windows Data Types).

So, the correct declaration of your functions would be:

unsigned long __stdcall printer_thread(void *args);
unsigned long __stdcall receiver_thread(void *args);
unsigned long __stdcall serverconn_thread(void *args);

但是，由于 CreateThread() 采用 LPTHREAD_START_ROUTINE 作为输入，该输入被声明为 DWORD (WINAPI*)(LPVOID)(请参阅winbase.h 中的实际声明)，您应该声明您的函数以匹配:

DWORD WINAPI printer_thread(LPVOID args);
DWORD WINAPI receiver_thread(LPVOID args);
DWORD WINAPI serverconn_thread(LPVOID args);