Problem joining char* to filesystem::path.filename() or char[260]

Question

I Know similar questions have been asked before but none of them Helped in my case.

Basically I want dstPath = %AppData% + "CURRENT EXE NAME"

but problem is with different string types and string concantation

SIMPLIFIED CODE :-

#include <stdio.h>
#include <string>
#include <filesystem>

#include <Shlwapi.h>
#include <Windows.h>

using namespace std;

int main()
{
    TCHAR selfPath[MAX_PATH];
    TCHAR dstPath[MAX_PATH];
    
    if (GetModuleFileName(NULL, selfPath, MAX_PATH) == 0)       // Getting exe File Location
        printf("Error : %ul\n", GetLastError());
    
    filesystem::path p(selfPath);
    
    dstPath = strcat(getenv("APPDATA"), p.filename().string().c_str());     // Here Comes The Error
    
    printf("Src : %s\n", selfPath);
    printf("Dst : %s\n", dstPath);
    
    return 0;
}

COMPILER COMMAND :-

g++ -Os -s -o ./builds/gcc-rat-x64.exe ./source/rat.cpp -std=c++17 -m64 -lshlwapi

COMPILER ERROR :-

error: incompatible types in assignment of 'char*' to 'TCHAR [260]' {aka 'char [260]'}
   80 |  dstPath = strcat(getenv("APPDATA"), p.filename().string().c_str());

Answer 1

You cannot assign to arrays. You should use strcpy() to copy C-style strings.

strcpy(dstPath, getenv("APPDATA"));
strcat(dstPath, p.filename().string().c_str());

Or the concatination can be done in one line via snprintf():

snprintf(dstPath, sizeof(dstPath), "%s%s", getenv("APPDATA"), p.filename().string().c_str());

Finally, TCHAR and GetModuleFileName can refer to UNICODE version of the API, according to the compilation option. Using ANSI version (char and GetModuleFileNameA) explicitly is safer to work with std::string and other APIs that require strings consists of char.

Answer 2

You are trying to use strcat to concatenate two strings and store the result in another one, but it does not work that way. The call strcat (str1, str2) adds the content of str2 at the end of str1. It also returns a pointer to str1 but I don't normally use it.

What you are trying to do should be done in three steps:

• Make sure that dstPath contains an empty string
• Concatenate to dstPath the value of the environment variable APPDATA
• Concatenate to dstPath the value of filename

Something like this:

dstPath[0] = '\0';
strcat(dstPath, getenv("APPDATA"));
strcat(dstPath, p.filename().string().c_str());

You should also add checks not to overflow dstPath...

Answer 3

First off, you are mixing TCHAR and char APIs in a way you should not be. You really should not be using TCHAR at all in modern code. But, if you are going to use TCHAR, then at least use TCHAR- based functions/macros, like _tprintf() instead of printf(), _tcscat() instead of strcat(), etc.

The compiler error is because you are trying to assign the char* pointer returned by strcat() to your dstPath TCHAR[] array. You can't assign a pointer to an array like that. You should strcpy() the result of getenv() into dstPath first, and then strcat() your filename onto the end of it, eg:

#include <string>
#include <filesystem>

#include <Windows.h>
#include <Shlwapi.h>
#include <stdio.h>
#include <tchar.h>

TCHAR* _tgetenv(const TCHAR *varname)
{
    #ifdef _UNICODE
    return _wgetenv(varname);
    #else
    return getenv(varname);
    #endif
}

std::basic_string<TCHAR> path2TStr(const std::filesystem::path &p)
{
    #ifdef _UNICODE
    return p.wstring();
    #else
    return p.string();
    #endif
}

int main()
{
    TCHAR selfPath[MAX_PATH];
    TCHAR dstPath[MAX_PATH];
    
    if (GetModuleFileName(NULL, selfPath, MAX_PATH) == 0)       // Getting exe File Location
    {
        printf("Error : %ul\n", GetLastError());
        return 0;
    }

    std::filesystem::path p(selfPath);
    
    _tcscpy(dstPath, _tgetenv(_T("APPDATA")));
    _tcscat(dstPath, path2TStr(p.filename()).c_str());
    
    _tprintf(_T("Src : %s\n"), selfPath);
    _tprintf(_T("Dst : %s\n"), dstPath);
    
    return 0;
}

However, you really should be using SHGetFolderPath(CSIDL_APPDATA) or SHGetKnownFolderPath(FOLDERID_RoamingAppData) instead of using getenv("APPDATA").

And since you are using the <filesystem> library anyway, you really should just use std::filesystem::path for all of your path handling. It has operator/= and operator/ to concatenate path segments, and an operator<< for printing paths to a std::ostream, like std::cout. Don't use strcat() for concatenating path segments, it won't handle directory separators correctly, at least.

Try this instead:

#include <iostream>
#include <string>
#include <filesystem>
#include <stdexcept>

#include <Windows.h>
#include <Shlobj.h>

std::filesystem::path getSelfPath()
{
    WCHAR wPath[MAX_PATH] = {};
    
    if (!GetModuleFileNameW(NULL, wPath, MAX_PATH))       // Getting exe File Location
    {
        DWORD err = GetLastError();
        throw std::runtime_error("Error : " << std::to_string(err));
    }

    return wPath;
}

std::filesystem::path getAppDataPath()
{
    WCHAR wPath[MAX_PATH] = {};
    
    HRESULT hRes = SHGetFolderPathW(NULL, CSIDL_APPDATA, NULL, SHGFP_TYPE_CURRENT, wPath);       // Getting APPDATA Folder Location
    if (hRes != S_OK)
        throw std::runtime_error("Error : " << std::to_string(hRes));

    return wPath;
}

int main()
{
    try
    {
        auto selfPath = getSelfPath();
        auto dstPath = getAppDataPath() / selfPath.filename();
    
        std::cout << "Src : " << selfPath << "\n";
        std::cout << "Dst : " << dstPath << "\n";
    }
    catch (const std::exception &e)
    {
        std::cerr << e.what() << "\n";
    }
    
    return 0;
}