string conversion

ginjikun

Hi All! just wanted to ask, if i have a function which expects a LPCTSTR.. is it ok to call it as shown below func(LPCTSTR lp) { .... } 1) CString str="something"; func(str); 2) LPWSTR str="something"; <-- just a sample, not sure how to set a LPWSTR type func((LPCTSTR)str); thanks! me

David Crow

ginjikun wrote:

is it ok to call it as shown below

Coding schemes aside, yes. If it wasn't, the compiler would surely complain.

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CPallini

one is OK. 2) is bad, since it will work only on UNICODE builds. it is better:

LPTSTR str = _T("something");
func(str);

BTW: The L prefix does the magic for wide character literals, for instance

LPWSTR str = L"something"

:)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke

Rajkumar R

ginjikun wrote:

CString str="something"; func(str);

ok.

ginjikun wrote:

LPWSTR str="something"; <-- just a sample, not sure how to set a LPWSTR type

LPWSTR str = L"something"; LPCWSTR str = L"something";

ginjikun wrote:

func((LPCTSTR)str);

requires care. in this case if your project is unicode, it is safe.

ginjikun

hi Rajkumar R, what if the project is compile with _MBCS? will it still be ok? thanks

ginjikun

Hi, thanks for the reply! the assignment is just a sample.. however i am more concern with how FUNC is being called. you mentioned it will work only on UNICODE. what if the project is compiled with _MBCS, will FUNC((LPCTSTR)str) still work? thanks! me

CPallini

if you define _MBCS instead of _UNICODE then FUNC((LPCTSTR)str) expects const char * but you're passing instead a const wchar_t *. the pointer types are quite different and you're forcing the latter into the former with static cast, i.e. mistake. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke

Rajkumar R

No, it is not ok. My previous statements is still correct. func((LPCTSTR)str); requires care. in this case if your project is unicode, it is safe.

ginjikun wrote:

what if the project is compile with _MBCS? will it still be ok?

with the project settings, whenever the LPCTSTR is defined as LPCWSTR it is safe, as the str is of type LPWSTR. AFAIK, MBCS is not wide character, so passing wide character to function taking MBCS is not safe. mostly, Wide character and single character is used without any precautions simply using generic text mapping functions, but MBCS requires additional handling like (You must keep track of which bytes are lead bytes).

Hamid Taebi

And see The Complete Guide to C++ Strings, Part II - String Wrapper Classes[^].

ginjikun

Hi, thanks again. since it is an mfc project i just cast it to CString instead. func((CString)LPWSTR) i think this should be ok... ??? me

CPallini

ginjikun wrote:

i think this should be ok... ???

That works thanks to temporary CString object's constructor (it perforforms the conversion). :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke