CODEWITHSUNDEEP
c++type-conversionconst-char
burtek
burtek

Reputation: 2685

How to convert const char* to const WCHAR*

I have something like this:

if(GetFileAttributesW("C:\\Directory")!="INVALID_FILE_ATTRIBUTES") {...}

I get error: cannot convert 'const char*' to 'const WCHAR*' for argument '1' to 'DWORD GetFileAttributesW(const WCHAR*)'

How to convert const char* to const WCHAR*?

Upvotes: 3

Views: 3179

Answers (3)

PaperBirdMaster
PaperBirdMaster

Reputation: 13298

You're mixing text literals of one kind of codification with function calls with another kind of codification.

All this confusion is due the obscure chain of #defines and typedefs that Microsoft puts on his headers.

One of this annoying Microsofts tricks is to declare two function calls differenced with a letter A or W depending of the project settings. There's a macro that transforms the GetFileAttributes to GetFileAttributesA or GetFileAttributesW if UNICODE is defined.

In your case, you're getting rid of the macro and calling the UNICODE version directly (the one ended with the letter W) but in your call you're using a no-widestring literal, you can fix it easily appending a L to the literal (as suggested by other users):

if(GetFileAttributesW(L"C:\\Directory")!="INVALID_FILE_ATTRIBUTES") {...}

So, if you're calling the version ended with A, you can use a no-widestring literal:

if(GetFileAttributesA("C:\\Directory")!="INVALID_FILE_ATTRIBUTES") {...}

Other way to fix it is using the _T macro (Check this answer):

if(GetFileAttributesW(_T("C:\\Directory"))!="INVALID_FILE_ATTRIBUTES") {...}

But if UNICODE isn't defined, your original problem will rise again; finally, you can surrender to the Microsoft way of doing things and use all the macros provided:

// Note the lack of W or A, it's a macro, not a function call!!
if(GetFileAttributes(_T("C:\\Directory"))!="INVALID_FILE_ATTRIBUTES") {...}

Using the two macros (the one that changes GetFileAttributes with the UNICODE or no-UNICODE version and the one that appends the L to the literal), there's no need to worry about the project settings because the macros takes this responsability for you.

Edit.

My bad, i almost forget the most important part.

As pointed by other users, you're comparing the return value of GetFileAttributes with a text literal; it returns a DWORD and according to the Microsoft documentation:

A DWORD is a 32-bit unsigned integer (range: 0 through 4294967295 decimal).

So, in the end, you're comparing an integer with a char[24], the comparison is possible but, it will never be true! You must read about the function and how to use it ;)

Upvotes: 1

Remus Rusanu
Remus Rusanu

Reputation: 294437

Don't use GetFileAttributesW, use GetFileAttributes. Add _T to all const strings, and use _TCHAR*. And INVALID_FILE_ATTRIBUES is definitely not a string...

if(GetFileAttributes(_T("C:\\Directory"))!= INVALID_FILE_ATTRIBUTES ) 
 {...}

See Unicode Programming Summary.

Upvotes: 3

mschmoock
mschmoock

Reputation: 20884

You are trying to compare the pointers address rather than the comtent!

Check function: memcmp(...)

Upvotes: 0

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