Cannot add TCHAR* to const char

Question

Hello I'm trying to make my application to run on startup, and to do this to work on my clients PC firstly I needed to get their PC username, but when I'm trying to make this working I'm getting this error :

E2140 expression must have integral or unscoped enum type

Here's the code:

HKEY hKey;
const char* czStartName = "MY application";
TCHAR pcusername[UNLEN + 1];
DWORD pcusername_len = UNLEN + 1;
GetUserName((TCHAR*)pcusername, &pcusername_len);
const char* czExePath = "\"C:\\Users\\" + pcusername + "\\Desktop\\Myapplication.exe\" /background";

How Can I convert TCHAR* to Const Char?

You are adding pointers together. Adding pointers to strings together does not concatenate those strings. — François Andrieux, Sep 06 '17 at 19:36
@FrançoisAndrieux how to fix it? Could you answer with the code? — A.Krasniqi, Sep 06 '17 at 19:38
Use a `std::string` if you want to concatenate using the `+` operator, then you can pass it to any C functions using the `str.c_str()` method. Otherwise you need to use `strcat()`. — Dan, Sep 06 '17 at 19:40
[`std::string` likely helps here.](http://en.cppreference.com/w/cpp/string/basic_string) — user4581301, Sep 06 '17 at 19:40
Possible duplicate of [const char\* concatenation](https://stackoverflow.com/questions/1995053/const-char-concatenation) — Dan, Sep 06 '17 at 19:41
One possible solution: `const TCHAR* czStartName = _T("MY application"); std::wstring ws = std::wstring(czStartName) + pcusername;` use `ws.c_str()` to get concatanated string — marcinj, Sep 06 '17 at 19:41
@marcinj I got many errors : `"identifier "_T" is undefined"` , `no instance of constructor "std::basic_string<_Elem, _Traits, _Alloc>::basic_string [with _Elem=wchar_t, _Traits=std::char_traits, _Alloc=std::allocator]" matches the argument list` , `no operator "+" matches these operands` — A.Krasniqi, Sep 06 '17 at 19:49
@A.Krasniqi that is not an answer to copy paste, just an idea what to do. — marcinj, Sep 06 '17 at 19:51
Could anyone answer the answer with code? I tried your comments advice, but noone worked! — A.Krasniqi, Sep 06 '17 at 20:05
@Dan C++ places heavy duties on imports in spite of generally being quite inclusive. — user4581301, Sep 06 '17 at 20:09
Use [`SHGetKnownFolderPath`](https://msdn.microsoft.com/en-us/library/windows/desktop/bb762188(v=vs.85).aspx) to reliably get the path to a user's desktop folder. — molbdnilo, Sep 06 '17 at 20:47
@molbdnilo you probably just [solved X when the question asks Y](http://xyproblem.info/). Probably should be the *real* answer to this question. — Dan, Sep 06 '17 at 20:53
@Dan, good point. The error message referrd to one thing while the OP asks about another. — Brad S., Sep 06 '17 at 20:58

score 1 · Accepted Answer · edited Sep 06 '17 at 23:29

1

As others have said in the comments, you cannot concatenate strings in C using the addition operator. You can do something like in this example:

#include <string.h>

char buf[4096];
snprintf(buf, sizeof(buf), "\"C:\\Users\\%s\\Desktop\\Myapplication.exe\" /background", username);

const char* czExePath = buf;

edited Sep 06 '17 at 23:29

Dan

4,488
5
48
75

answered Sep 06 '17 at 20:55

Brad S.

327
1
9

Worked! Thank you – A.Krasniqi Sep 06 '17 at 21:33
2

Depending on C:\\Users\\username being that user's profile directory is a bad idea. It won't always be true. – Joshua Sep 07 '17 at 00:46
@Joshua, yes. of course. This little example is imperfect but it directly addresses the compiler error in the question. There are several other issues for sure. – Brad S. Sep 07 '17 at 02:07
@Joshua , in which cases it will be not true? – A.Krasniqi Sep 07 '17 at 13:12
@A.Krasniqi: It's still *possible* the user directory isn't c:\users; and if c:\users\username directory already exists before the user has logged in the first time that user will be given another directory. – Joshua Sep 07 '17 at 15:17
1

@A.Krasniqi: Always use SHGetSpecialFolderPath function for this job https://msdn.microsoft.com/en-us/library/windows/desktop/bb762204(v=vs.85).aspx – Joshua Sep 07 '17 at 15:18

Cannot add TCHAR* to const char

1 Answers1