digitalmars.D.learn - A weird example of .toUTF16z concatination side-effects in wcsncat
- BoQsc (38/38) Apr 07 2022 Here I try to concatenate three character strings using
- Tejas (6/9) Apr 07 2022 Maybe try using `wstring` instead of string? Also use the `w`
- BoQsc (27/37) Apr 07 2022 Exactly same results. `AAAAAAAAAABBBBBBBBBBBBBBBBBBBB`
- Stanislav Blinov (16/20) Apr 07 2022 You're witnessing undefined behavior. "AAAAAAAAAA" is a string
- BoQsc (32/52) Apr 07 2022 That is correct, the results are satisfying. I believe this
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`
Apr 07 2022
On Thursday, 7 April 2022 at 10:50:35 UTC, BoQsc wrote:Here I try to concatenate three character strings using `wcsncat()`. [...]Maybe try using `wstring` instead of string? Also use the `w` postfix ```d wstring dlang_string = "BBBBBBBBBBB"w; I can't test because I'm not on my PC and I don't use Windows
Apr 07 2022
BoQsc <vaidas.boqsc gmail.com> On Thursday, 7 April 2022 at 11:03:39 UTC, Tejas wrote:On Thursday, 7 April 2022 at 10:50:35 UTC, BoQsc wrote: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 } ```Here I try to concatenate three character strings using `wcsncat()`. [...]Maybe try using `wstring` instead of string? Also use the `w` postfix ```d wstring dlang_string = "BBBBBBBBBBB"w; I can't test because I'm not on my PC and I don't use Windows
Apr 07 2022
On Thursday, 7 April 2022 at 10:50:35 UTC, BoQsc wrote:wchar_t* clang_string = cast(wchar_t *)"AAAAAAAAAA";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`:The behavior is undefined if the destination array is not large enough for the contents of both str and dest and the terminating null wide character.`wcsncat` does not allocate memory, it expects you to provide a sufficiently large mutable buffer. For example, like this: ```d // ... auto cls = new wchar_t[256]; cls[] = 0; cls[0..10] = 'A'; wchar_t* clang_string = cls.ptr; // ... ```
Apr 07 2022
On Thursday, 7 April 2022 at 12:51:26 UTC, Stanislav Blinov wrote:On Thursday, 7 April 2022 at 10:50:35 UTC, BoQsc wrote: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 } ```wchar_t* clang_string = cast(wchar_t *)"AAAAAAAAAA";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`:The behavior is undefined if the destination array is not large enough for the contents of both str and dest and the terminating null wide character.`wcsncat` does not allocate memory, it expects you to provide a sufficiently large mutable buffer. For example, like this: ```d // ... auto cls = new wchar_t[256]; cls[] = 0; cls[0..10] = 'A'; wchar_t* clang_string = cls.ptr; // ... ```
Apr 07 2022