CODEWITHSUNDEEP
c++
Andrew Wilson
Andrew Wilson

Reputation: 157

How to concatenate a LPCWSTR?

How would I take...

string modelPath = "blah/blah.obj"

and concatenate it with...

L" not found."

While passing it in as LPCWSTR. I tried to do

(LPCWSTR)(modelPath + " was not found.").c_str()

However that did not work. Here is a larger example of what it looks like now.

if(!fin)
{
    MessageBox(0, L"Models/WheelFinal.txt not found.", 0, 0); //
    return;
}

Upvotes: 3

Views: 4845

Answers (2)

Qix - MONICA WAS MISTREATED
Qix - MONICA WAS MISTREATED

Reputation: 15153

LPCWSTR is a L ong P ointer to a C onstant W ide STR ing. Wide strings, at least in Win32, are 16 bits, whereas (const) char strings (i.e. (C)STR or their pointer-counterparts LP(C)STR) are 8 bits.

Think of them on Win32 as typedef const char* LPCSTR and typedef const wchar_t* LPCWSTR.

std::string is an 8-bit string (using the underlying type char by default) whereas std::wstring is a wider character string (i.e. 16-bits on win32, using wchar_t by default).

If you can, use std::wstring to concatenate a L"string" as a drop-in replacement.

A note on MessageBox()

Windows has a funny habit of defining macros for API calls that switch out underlying calls given the program's multibyte configuration. For almost every API call that uses strings, there is a FunctionA and FunctionW call that takes an LPCSTR or LPWCSTR respectively.

MessageBox is one of them. In Visual Studio, you can go into project settings and change your Multi-Byte (wide/narrow) setting or you can simply call MessageBoxA/W directly in order to pass in different encodings of strings.

For example:

LPWCSTR wideString = L"Hello, ";
MessageBoxW(NULL, (std::wstring(wideString) + L"world!").c_str(), L"Hello!", MB_OK);

LPCSTR narrowString = "Hello, ";
MessageBoxA(NULL, (std::string(narrowString) + "world!").c_str(), "Hello!", MB_OK);

Upvotes: 4

Qaz
Qaz

Reputation: 61970

If you can change modelPath to std::wstring, it becomes easy:

MessageBox(nullptr, (modelPath + L" not found.").c_str(), nullptr, 0);

I changed your 0 pointer values into nullptr as well.

Since std::string represents a narrow string, std::wstring represents a wide string, and the two are wildly different, casting from one representation to the other does not work, while starting with the appropriate one does. On the other hand, one can properly convert between representations using the new <codecvt> header in C++11.

Upvotes: 3

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