wchar parameters using boost or the Standard Library

Question

How can I make this code use the boost C++ string library or the Standard Library, to avoid wchar_t size definition, and to have a more dynamic string which can be processed much easier? This code uses MFC's CString, but I would prefer to use the Standard Library or boost instead.

TCHAR       drive[_MAX_DRIVE];
TCHAR       dir[_MAX_DIR];
TCHAR       fname[_MAX_FNAME];
TCHAR       ext[_MAX_EXT];
CString     cstr;

GetModuleFileName(NULL,cstr.GetBuffer(MAX_PATH),MAX_PATH);
cstr.ReleaseBuffer();

_wsplitpath_s(cstr,drive,dir,fname,ext);
cstr=drive;
cstr+=dir;
cstr+=_T("\\myfile.dat");

Answer 1

You should have a look at the C++ standard <filesystem> library, specifically its path class, which has a replace_filename() method, eg:

#include <filesystem>
#include <windows.h>

WCHAR szFileName[MAX_PATH] = {};
GetModuleFileNameW(NULL, szFileName, MAX_PATH);
std:wstring str = std::filesystem::path(szFileName).replace_filename(L"myfile.dat").wstring();

Or, since you are using the Win32 API anyway, you could simply use PathRemoveFileSpec() and PathAppend() instead (or their safer Cch counterparts), eg:

#include <windows.h>

WCHAR szFileName[MAX_PATH] = {};
GetModuleFileNameW(NULL, szFileName, MAX_PATH);
PathRemoveFileSpecW(szFileName);
PathAppendW(szFileName, L"myfile.dat");
std:wstring str = szFileName;

If you really want to avoid the MAX_PATH restriction, you will have to call GetModuleFileName() in a loop, increasing the size of the buffer on each iteration, until it finally succeeds:

std::wstring wFileName(MAX_PATH, L'\0');
do {
    DWORD dwSize = GetModuleFileNameW(NULL, wFileName.data(), wFileName.size()); // or &wFileName[0] before C++17
    if (dwSize < wFileName.size()) {
        wFileName.resize(dwSize);
        break;
    }
    wFileName.resize(wFileName.size() * 2);
}
while (true);
// use wFileName as needed...