What Is wrong with this code?

Question

What Is wrong with this code?

CDev-8220 365

I getting this error on the function below, which is not already defined, as far as I know.

Error:

Warning: discarding return value of function with [[nodiscard]] attribute Error: "class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __cdecl WCHAR_TO_STRING(wchar_t *,int &)" (?WCHAR_TO_STRING@@YA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@PEA_WAEAH@Z) already defined in WinApp.obj Error: one or more multiply defined symbols found

Code:

string WCHAR_TO_STRING(WCHAR* wc, int& chars) {
	string ws = "";
	return ws;
}

I don't understand why.

Can someone please explain. Thanks.

Viorel 122.6K Reputation points

2025-03-17T16:16:12.45+00:00

Add inline (inline string WCHAR_TO_STRING(WCHAR* wc....) and continue investigations.
CDev-8220 365 Reputation points

2025-03-17T22:30:54.1566667+00:00

That caused the error to go away, but why?

Also, I have about 16 lines of code in the function, so would it be ideal to make it inline?

Not that I am complaining. I just want to understand what's happening.

Thanks.
Viorel 122.6K Reputation points

2025-03-18T09:06:34.14+00:00
It seems that the function was defined inside a header (.h) file, and there are several #include directives that simply paste the same code to multiple source files, which cause the errors. To solve the problem, you can add static — static string WCHAR_TO_STRING(.... — however this could result in code duplication (multiple local WCHAR_TO_STRING functions, larger program). I think that inline is more appropriate for short functions.

The traditional approach is to split the declarations and definitions:

// in "MyFunctions.h" file: string WCHAR_TO_STRING(WCHAR* wc, int& chars);

// in one .cpp file, for example: "MyFunctions.cpp": #include "MyFunctions.h" string WCHAR_TO_STRING(WCHAR* wc, int& chars) { string ws = ""; return ws; }

// in other CPP files: #include "MyFunctions.h" void test1() { // use the function: string s = WCHAR_TO_STRING(.....); }

See also another modern approach:

// In "MyFunctions.h" (the "MyFunctions.cpp" is not needed): namespace // unnamed namespace { string WCHAR_TO_STRING(WCHAR* wc, int& chars) { string ws = ""; return ws; } }
Minxin Yu 13,501 Reputation points Microsoft External Staff

2025-03-20T03:07:36.5233333+00:00

Haven't heard from you for a while. Have you solved your issue?
CDev-8220 365 Reputation points

2025-03-20T04:23:15.2133333+00:00

It seems that the function was defined inside a header (.h) file, and there are several #include directives that simply paste the same code to multiple source files

The function definition is included in header file. And #include header.h in multiple .cpp files causes duplicate symbol definitions.

Sorry. I was still scratching my head.

I suppose you did tell me what happened, but I don't think you explained why it happened - i.e. why some random foolish name function gets duplicated, and not the 20 others in the same header file.

Perhaps I 'll find out later.

At least I know the solution.

Thanks.

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Viorel 122.6K Reputation points

2025-03-17T16:16:12.45+00:00

Add inline (inline string WCHAR_TO_STRING(WCHAR* wc....) and continue investigations.
CDev-8220 365 Reputation points

2025-03-17T22:30:54.1566667+00:00

That caused the error to go away, but why?

Also, I have about 16 lines of code in the function, so would it be ideal to make it inline?

Not that I am complaining. I just want to understand what's happening.

Thanks.
Viorel 122.6K Reputation points

2025-03-18T09:06:34.14+00:00

It seems that the function was defined inside a header (.h) file, and there are several #include directives that simply paste the same code to multiple source files, which cause the errors. To solve the problem, you can add static — static string WCHAR_TO_STRING(.... — however this could result in code duplication (multiple local WCHAR_TO_STRING functions, larger program). I think that inline is more appropriate for short functions.

The traditional approach is to split the declarations and definitions:

// in "MyFunctions.h" file: string WCHAR_TO_STRING(WCHAR* wc, int& chars);

// in one .cpp file, for example: "MyFunctions.cpp": #include "MyFunctions.h" string WCHAR_TO_STRING(WCHAR* wc, int& chars) { string ws = ""; return ws; }

// in other CPP files: #include "MyFunctions.h" void test1() { // use the function: string s = WCHAR_TO_STRING(.....); }

See also another modern approach:

// In "MyFunctions.h" (the "MyFunctions.cpp" is not needed): namespace // unnamed namespace { string WCHAR_TO_STRING(WCHAR* wc, int& chars) { string ws = ""; return ws; } }
Minxin Yu 13,501 Reputation points Microsoft External Staff

2025-03-20T03:07:36.5233333+00:00

Haven't heard from you for a while. Have you solved your issue?
CDev-8220 365 Reputation points

2025-03-20T04:23:15.2133333+00:00

It seems that the function was defined inside a header (.h) file, and there are several #include directives that simply paste the same code to multiple source files

The function definition is included in header file. And #include header.h in multiple .cpp files causes duplicate symbol definitions.

Sorry. I was still scratching my head.

I suppose you did tell me what happened, but I don't think you explained why it happened - i.e. why some random foolish name function gets duplicated, and not the 20 others in the same header file.

Perhaps I 'll find out later.

At least I know the solution.

Thanks.

Answer 1

Hi,

The function definition is included in header file. And #include header.h in multiple .cpp files causes duplicate symbol definitions.

inline keywords explicitly allows multiple definitions.

Best regards,

Minxin Yu

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