C++ Builder 10.3 无法从 const char[18] 分配给 const wchar_t*

Question

I have a simple code for directories handling, and here is a part of it. The problem is, that in older version of builder(I guess it is 6) it was working perfectly, now it throws [bcc32c Error] Unit1.cpp(32): assigning to 'PCZZWSTR' (aka 'const wchar_t *') from incompatible type 'const char [18]' .

void __fastcall TForm1::Button2Click(TObject *Sender)
{
SHFILEOPSTRUCT fos;
String dirDest;
fos.hwnd = Handle;
//operacja kopiowania
fos.wFunc = FO_COPY;
//plik źródłowy
fos.pFrom = "C:\\Melon\\AGA\\Bazy";
}

The problem is with line fos.pFrom = "C:\\\\Melon\\\\AGA\\\\Bazy"; . I tried assigning "C:\\\\Melon\\\\AGA\\\\Bazy" to const wchar_t* using linkig, but it thrown me that it can not be linked. Does somebody have a clue how to fix it?

Answer 1

You are using the TCHAR -based version of SHFILEOPSTRUCT , so its string fields will be based on either wchar_t or char depending on whether UNICODE is defined or not, respectively.

In C++Builder 6 (where String was an alias for AnsiString ), UNICODE was not defined by default. In C++Builder 2009 onward (where String is an alias for UnicodeString ), UNICODE is defined by default, but can be turned off if needed for legacy projects.

Since you are using a TCHAR -based struct, you should use the TCHAR -based TEXT() macro when defining string literals for it, eg:

void __fastcall TForm1::Button2Click(TObject *Sender)
{
    SHFILEOPSTRUCT fos;
    fos.hwnd = Handle;
    //operacja kopiowania
    fos.wFunc = FO_COPY;
    //plik źródłowy
    fos.pFrom = TEXT("C:\\Melon\\AGA\\Bazy\0"); // don't forget the extra null terminator!
    fos.pTo = TEXT("...\0");
    ...
    SHFileOperation(&fos);
}

That will work in all C++Builder versions.

On the other hand, if you are trying to use a String variable to define strings for the struct, that will work only if UNICODE is undefined in pre-2009 versions, and defined in post-2009 versions, eg:

void __fastcall TForm1::Button2Click(TObject *Sender)
{
    String dirSrc("C:\\Melon\\AGA\\Bazy\0", 18); // don't forget the extra null terminator!
    String disDest(...);
    SHFILEOPSTRUCT fos;
    fos.hwnd = Handle;
    //operacja kopiowania
    fos.wFunc = FO_COPY;
    //plik źródłowy
    fos.pFrom = dirSrc.c_str();
    fos.pTo = dirDest.c_str();
    ...
    SHFileOperation(&fos);
}

If you don't want to rely on the UNICODE define, then you should use the ANSI or Unicode version of SHFILEOPSTRUCT explicitly, depending on whether you are working with ANSI ( char ) or Unicode ( wchar_t ) strings, eg:

void __fastcall TForm1::Button2Click(TObject *Sender)
{
    SHFILEOPSTRUCTA fos;
    fos.hwnd = Handle;
    //operacja kopiowania
    fos.wFunc = FO_COPY;
    //plik źródłowy
    fos.pFrom = "C:\\Melon\\AGA\\Bazy\0"; // don't forget the extra null terminator!
    fos.pTo = "...\0";
    ...
    SHFileOperationA(&fos);
}

void __fastcall TForm1::Button2Click(TObject *Sender)
{
    SHFILEOPSTRUCTW fos;
    fos.hwnd = Handle;
    //operacja kopiowania
    fos.wFunc = FO_COPY;
    //plik źródłowy
    fos.pFrom = L"C:\\Melon\\AGA\\Bazy\0"; // don't forget the extra null terminator!
    fos.pTo = L"...\0";
    ...
    SHFileOperationW(&fos);
}