Here I try to concatenate three character strings using wcsncat().

clang_string AAAAAAAAAA
dlang_string BBBBBBBBBBB
winpointer_to_string CCCCCCCCCC

import std.stdio;

@system void main(){

	import std.utf                : toUTF16z, toUTF16;
	import core.stdc.wchar_       : wcsncat, wcslen, wprintf;
	import core.stdc.stdlib       : wchar_t;
	import core.sys.windows.winnt : LPCWSTR;

	wchar_t* clang_string         = cast(wchar_t *)"AAAAAAAAAA";
	string   dlang_string         = "BBBBBBBBBBB";
	LPCWSTR  winpointer_to_string = "CCCCCCCCCC";
	
	wcsncat(clang_string, dlang_string.toUTF16z, wcslen(dlang_string.toUTF16z));
	//   String output: AAAAAAAAAABBBBBBBBBBB
	
	wcsncat(clang_string, winpointer_to_string, wcslen(winpointer_to_string));
	//   String output: AAAAAAAAAABBBBBBBBBBBBBBBBBBBB
	// Expected string: AAAAAAAAAABBBBBBBBBBBCCCCCCCCCC

	wprintf(clang_string);
	//   String output: AAAAAAAAAABBBBBBBBBBBBBBBBBBBB
	// Expected string: AAAAAAAAAABBBBBBBBBBBCCCCCCCCCC

}

Problem:
Any following concatenated string after "wcsncat() concatenation of dlang_string.toUTF16z string", happen to not be printed and gets overwritten.

The Expected output:
I was expecting the wprintf() result to be AAAAAAAAAABBBBBBBBBBBCCCCCCCCCC
The wprintf() result I've received is this: AAAAAAAAAABBBBBBBBBBBBBBBBBBBB

On Thursday, 7 April 2022 at 10:50:35 UTC, BoQsc wrote:

Maybe try using wstring instead of string? Also use the w postfix

wstring dlang_string = "BBBBBBBBBBB"w;

I can't test because I'm not on my PC and I don't use Windows

On Thursday, 7 April 2022 at 11:03:39 UTC, Tejas wrote:

wstring dlang_string = "BBBBBBBBBBB"w;

I can't test because I'm not on my PC and I don't use Windows

Exactly same results. AAAAAAAAAABBBBBBBBBBBBBBBBBBBB

import std.stdio;

@system void main(){

	import std.utf                : toUTF16z, toUTF16;
	import core.stdc.wchar_       : wcsncat, wcslen, wprintf;
	import core.stdc.stdlib       : wchar_t;
	import core.sys.windows.winnt : LPCWSTR;

	wchar_t*  clang_string         = cast(wchar_t *)"AAAAAAAAAA";
	wstring   dlang_string         = "BBBBBBBBBBB"w; //<---- NEW, same results
	LPCWSTR   winpointer_to_string = "CCCCCCCCCC";
	
	wcsncat(clang_string, dlang_string.toUTF16z, wcslen(dlang_string.toUTF16z));
	//   String output: AAAAAAAAAABBBBBBBBBBB
	
	wcsncat(clang_string, winpointer_to_string, wcslen(winpointer_to_string));
	//   String output: AAAAAAAAAABBBBBBBBBBBBBBBBBBBB
	// Expected string: AAAAAAAAAABBBBBBBBBBBCCCCCCCCCC

	wprintf(clang_string);
	//   String output: AAAAAAAAAABBBBBBBBBBBBBBBBBBBB
	// Expected string: AAAAAAAAAABBBBBBBBBBBCCCCCCCCCC

}

On Thursday, 7 April 2022 at 10:50:35 UTC, BoQsc wrote:

You're witnessing undefined behavior. "AAAAAAAAAA" is a string literal and is stored in the data segment. Mere cast to wchar_t* does not make writing through that pointer legal. Moreover, even if it was legal to write through it, that alone wouldn't be sufficient. From documentation of wcsncat:

wcsncat does not allocate memory, it expects you to provide a sufficiently large mutable buffer. For example, like this:

    // ...
    auto cls = new wchar_t[256];
    cls[] = 0;
    cls[0..10] = 'A';
    wchar_t* clang_string = cls.ptr;
    // ...

On Thursday, 7 April 2022 at 12:51:26 UTC, Stanislav Blinov wrote:

    // ...
    auto cls = new wchar_t[256];
    cls[] = 0;
    cls[0..10] = 'A';
    wchar_t* clang_string = cls.ptr;
    // ...

That is correct, the results are satisfying. I believe this thread is resolved.

import std.stdio;

@system void main(){

	import std.utf                : toUTF16z, toUTF16;
	import core.stdc.wchar_       : wcsncat, wcslen, wprintf;
	import core.stdc.stdlib       : wchar_t;
	import core.sys.windows.winnt : LPCWSTR;


	auto cls = new wchar_t[256];
    cls[] = 0;
    cls[0..10] = 'A';
    wchar_t* clang_string = cls.ptr;

	//wchar_t*  clang_string         = cast(wchar_t *)"AAAAAAAAAA";
	wstring   dlang_string         = "BBBBBBBBBB"w; //<---- NEW, same results
	LPCWSTR   winpointer_to_string = "CCCCCCCCCC";
	
	wcsncat(clang_string, dlang_string.toUTF16z, wcslen(dlang_string.toUTF16z));
	//   String output: AAAAAAAAAABBBBBBBBBB
	
	wcsncat(clang_string, winpointer_to_string, wcslen(winpointer_to_string));
	//   String output: AAAAAAAAAABBBBBBBBBBCCCCCCCCCC
	// Expected string: AAAAAAAAAABBBBBBBBBBCCCCCCCCCC

	wprintf(clang_string);
	//   String output: AAAAAAAAAABBBBBBBBBBCCCCCCCCCC
	// Expected string: AAAAAAAAAABBBBBBBBBBCCCCCCCCCC

}