How to correctly pass a LPCSTR type parameter to a thread in DLL?
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I wrote a DLL with VC6.0. I want to pass a LPCSTR type parameter (file path) to a thread. Here is the code: DWORD WINAPI ThreadFunc(LPVOID lpParam) { char* fileLoct = (char*)lpParam; MessageBox(NULL, fileLoct, "Message", MB_OK | MB_ICONINFORMATION); return 0; } void __stdcall StartThread(LPCSTR flt) { HANDLE hThread; hThread = CreateThread(NULL, 0, ThreadFunc, (void *)flt, 0, NULL); CloseHandle(hThread); } I tested it with MessageBox and found the path was not correct at all. How to correctly pass a LPCSTR type parameter to a thread in DLL? Thank you.
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I wrote a DLL with VC6.0. I want to pass a LPCSTR type parameter (file path) to a thread. Here is the code: DWORD WINAPI ThreadFunc(LPVOID lpParam) { char* fileLoct = (char*)lpParam; MessageBox(NULL, fileLoct, "Message", MB_OK | MB_ICONINFORMATION); return 0; } void __stdcall StartThread(LPCSTR flt) { HANDLE hThread; hThread = CreateThread(NULL, 0, ThreadFunc, (void *)flt, 0, NULL); CloseHandle(hThread); } I tested it with MessageBox and found the path was not correct at all. How to correctly pass a LPCSTR type parameter to a thread in DLL? Thank you.
What was "not correct" about it?
The difficult we do right away... ...the impossible takes slightly longer.
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What was "not correct" about it?
The difficult we do right away... ...the impossible takes slightly longer.
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MessageBox display is not file path, instead it showed something "s" or "c", "7". this is what I don't understand.
Are you calling the thread from a Unicode function? If you're passing a Unicode string to a function that expects an ANSI string, this is what you'll see. See: Converting Unicode and ANSI Strings[^] and: WideCharToMultiByte function[^]
The difficult we do right away... ...the impossible takes slightly longer.
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Are you calling the thread from a Unicode function? If you're passing a Unicode string to a function that expects an ANSI string, this is what you'll see. See: Converting Unicode and ANSI Strings[^] and: WideCharToMultiByte function[^]
The difficult we do right away... ...the impossible takes slightly longer.
No, my function is not a Unicode function. my file path is C:\Downloads\HornSound.wav. I found if I added the following " MessageBox(NULL, loct, "Message1", NULL); " before "CloseHandle(hThread);". Both MessageBoxes (both in the function and in the thread) can correctly display the file path. But if I removed "MessageBox" in the function, then the MessageBox in the thread cannot correctly display the file path. What is the problem?
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I wrote a DLL with VC6.0. I want to pass a LPCSTR type parameter (file path) to a thread. Here is the code: DWORD WINAPI ThreadFunc(LPVOID lpParam) { char* fileLoct = (char*)lpParam; MessageBox(NULL, fileLoct, "Message", MB_OK | MB_ICONINFORMATION); return 0; } void __stdcall StartThread(LPCSTR flt) { HANDLE hThread; hThread = CreateThread(NULL, 0, ThreadFunc, (void *)flt, 0, NULL); CloseHandle(hThread); } I tested it with MessageBox and found the path was not correct at all. How to correctly pass a LPCSTR type parameter to a thread in DLL? Thank you.
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I wrote a DLL with VC6.0. I want to pass a LPCSTR type parameter (file path) to a thread. Here is the code: DWORD WINAPI ThreadFunc(LPVOID lpParam) { char* fileLoct = (char*)lpParam; MessageBox(NULL, fileLoct, "Message", MB_OK | MB_ICONINFORMATION); return 0; } void __stdcall StartThread(LPCSTR flt) { HANDLE hThread; hThread = CreateThread(NULL, 0, ThreadFunc, (void *)flt, 0, NULL); CloseHandle(hThread); } I tested it with MessageBox and found the path was not correct at all. How to correctly pass a LPCSTR type parameter to a thread in DLL? Thank you.
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I wrote a DLL with VC6.0. I want to pass a LPCSTR type parameter (file path) to a thread. Here is the code: DWORD WINAPI ThreadFunc(LPVOID lpParam) { char* fileLoct = (char*)lpParam; MessageBox(NULL, fileLoct, "Message", MB_OK | MB_ICONINFORMATION); return 0; } void __stdcall StartThread(LPCSTR flt) { HANDLE hThread; hThread = CreateThread(NULL, 0, ThreadFunc, (void *)flt, 0, NULL); CloseHandle(hThread); } I tested it with MessageBox and found the path was not correct at all. How to correctly pass a LPCSTR type parameter to a thread in DLL? Thank you.
What doesn't work? compiler error? What's the error? Runtime error? Describe it. Give people something to go on!
Steve
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What is thae value of
fltat the point that you call the thread, where does it come from?"flt" is the file path from VBA. it's "C:\Downloads\HornSound.wav." Sorry, it's my mistake. the "loct" in MessageBox should be replaced with "flt". I spent some time try to figure it out. So as I said, I added " MessageBox(NULL, flt, "Message1", NULL); " before "CloseHandle(hThread);". both messagebox can correctly display my file path "C:\Downloads\HornSound.wav." I also found if I replaced "MessageBox" with "Sleep(3000)" before "CloseHandle(hThread);" MessageBox in thread can correctly display my file path "C:\Downloads\HornSound.wav." if I add nothing and just removed "CloseHandle(hThread);", MessageBox in thread can also correctly display my file path "C:\Downloads\HornSound.wav." It seems I cannot close handle right after CreateThread. but that can cause memory leak?
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What doesn't work? compiler error? What's the error? Runtime error? Describe it. Give people something to go on!
Steve
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"flt" is the file path from VBA. it's "C:\Downloads\HornSound.wav." Sorry, it's my mistake. the "loct" in MessageBox should be replaced with "flt". I spent some time try to figure it out. So as I said, I added " MessageBox(NULL, flt, "Message1", NULL); " before "CloseHandle(hThread);". both messagebox can correctly display my file path "C:\Downloads\HornSound.wav." I also found if I replaced "MessageBox" with "Sleep(3000)" before "CloseHandle(hThread);" MessageBox in thread can correctly display my file path "C:\Downloads\HornSound.wav." if I add nothing and just removed "CloseHandle(hThread);", MessageBox in thread can also correctly display my file path "C:\Downloads\HornSound.wav." It seems I cannot close handle right after CreateThread. but that can cause memory leak?
The fact that it works when you add a delay suggests that the file path buffer is getting destroyed before the thread process has constructed the message box. You should ensure the buffer is preserved until the thread has finished using it, by some form of synchronisation. Or better still don't use threads unless they are serving some necessary function.
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I wrote a DLL with VC6.0. I want to pass a LPCSTR type parameter (file path) to a thread. Here is the code: DWORD WINAPI ThreadFunc(LPVOID lpParam) { char* fileLoct = (char*)lpParam; MessageBox(NULL, fileLoct, "Message", MB_OK | MB_ICONINFORMATION); return 0; } void __stdcall StartThread(LPCSTR flt) { HANDLE hThread; hThread = CreateThread(NULL, 0, ThreadFunc, (void *)flt, 0, NULL); CloseHandle(hThread); } I tested it with MessageBox and found the path was not correct at all. How to correctly pass a LPCSTR type parameter to a thread in DLL? Thank you.
You are using an automatic variable sent from VB call. That variable, and the string contente, will be destroyed after the function that create the thread returns. The thread instead will be running and looking for the string at the address that you passed in the thread creation, but that address holds only garbage by then... To make it work create a local string in your code and define it 'static', copy the passed string there, then create the thread.
void __stdcall StartThread(LPCSTR flt)
{
HANDLE hThread;
static char *szStaticString[MAX_PATH];
strncpy(szStaticString, flt, MAX_PATH-1);
hThread = CreateThread(NULL, 0, ThreadFunc,
(void *)szStaticString, 0, NULL);CloseHandle(hThread);
} -
You are using an automatic variable sent from VB call. That variable, and the string contente, will be destroyed after the function that create the thread returns. The thread instead will be running and looking for the string at the address that you passed in the thread creation, but that address holds only garbage by then... To make it work create a local string in your code and define it 'static', copy the passed string there, then create the thread.
void __stdcall StartThread(LPCSTR flt)
{
HANDLE hThread;
static char *szStaticString[MAX_PATH];
strncpy(szStaticString, flt, MAX_PATH-1);
hThread = CreateThread(NULL, 0, ThreadFunc,
(void *)szStaticString, 0, NULL);CloseHandle(hThread);
} -
I didn't realize that string variable was destroyed after the function creating the thread returns. Now my DLL works great. Frankie, thank you so much.