typecasting

FotisSs

Hi guys I have a simple question for your. Let say that I have CreateFile function that takes as a first argument a LPCTSTR pointer. Also there is a declared buffer as char* szBuffer . I' ve seen a lot of guys using a typecasting for calling CreateFile like this CreateFile((LPCTSTR)szBuffer,....). I simply use CreateFile(szBuffer,....) with no problems Is that typecasting needed, given that both char* and LPCTSTR are pointers. Are there any true gains by using typecasting? Thanx

Cedric Moonen

FotisSs wrote:

I' ve seen a lot of guys using a typecasting

Well, they were wrong... LPCTSTR is an array of TCHAR and the definition of a TCHAR depends if UNICODE is enabled or not. So, the code will work fine if UNICODE is not defined but it will not work if UNICODE is defined. In which case, if you have the typecast, it will simply be plain wrong (the string will be corrupted), but if you don't have the cast, then it will not compile (which is way better, because at least you don't have a nasty bug in your code). Typecasts should be avoided at maximum: using them too much means probably that you don't understand what you are doing. I suggest that you read this article[^], it explains a lot about character encoding (and about TCHAR).

Cédric Moonen Software developer
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Rajesh R Subramanian

Usage of things like char is what scaring me more than the typecasts. One should ideally use TCHAR instead, which is neutral to builds (and is defined as char in an ANSI build and as a wchar_t in an Unicode build). If an API expects an LPCTSTR, that means that it has both an ANSI and an Unicode implementation and the appropriate version will be called based on the build (for Unicode build, CreateFileW and for an ANSI build, CreateFileA will be called). There is no excuse to use char unless you're *sure* that you are always going to do an ANSI only build. Even then, I won't recommend it. Typecasting a char* to an LPCTSTR in an Unicode build is an invitation to disaster, because the wide version of the API will be called, which is going to expect a wchar_t*. There is no excuse to write such crap code.

“Follow your bliss.” – Joseph Campbell

FotisSs

ok my fault I always tend to use specifically CreateFileA so it is LPSTR! And the question remains is typecasting needed?

Rajesh R Subramanian

FotisSs wrote:

And the question remains is typecasting needed?

I haven't answered it? Take CreateFile for example, which expects an LPCTSTR If you have a TCHAR*, no typecasting is needed, or typecasting has no effect. If you have a char*, passing that to this function by casting it to an LPCTSTR will cause trouble in Unicode Build. If you have a wchar_t*, passing that to this function by casting it to an LPCTSTR will cause trouble in ANSI build. If you use TCHAR*, no casting will be needed at all, and the correct data type will be automatically used. I will also highly recommend that you read the article that the other poster gave you a link for! It's well worth the time you'll spend on it.

“Follow your bliss.” – Joseph Campbell

David Crow

FotisSs wrote:

Is that typecasting needed, given that both char* and LPCTSTR are pointers.

Unicode issues aside, no, and not because they are both pointers. It's because the function's signature will treat the pointer argument as a const and not change it. On the other hand, if you had a function that was expecting a LPTSTR and you were passing it a const pointer, then casting would be an issue.

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