I'm on linux/opensuse, trying to pass a wchar_* from C to D but I'm getting only the first letter of that string. Could someone help figure out why?

this is the piece of D code:

extern(C) export
void sayHello(const (wchar) *s)
{
	import std.stdio : writeln;
	import std.conv : to;

	import core.runtime : rt_init, rt_term;
	rt_init();
	scope(exit) rt_term();

	writeln("+sayHello()");
	auto s2 = to!string(s);
	writeln("s2 = ", s2);
	writeln("-sayHello()");
}

build with dub, using "targetType": "dynamicLibrary" in dub.json.

and below the piece of C code where I call the lib's function, compiled with clang -std=c11 -m64 dll.c -ldl


  const char *libpath = "path/to/library.so";
  void *lh = dlopen(libpath, RTLD_LAZY);
  if(!lh) {
    fprintf(stderr, "dlopen error: %s\n", dlerror());
    return EXIT_FAILURE;
  }

  const wchar_t *s2 = L"hello!";
  void (*fp)(const wchar_t*) = dlsym(lh, "sayHello");
  char *de = dlerror();
  if(de) {
    fprintf(stderr, "slsym error:%s\n", de);
    return EXIT_FAILURE;
  }
  fp(s2);

the output is "h" rather "hello". What am I missing?

On Wednesday, 9 December 2020 at 20:35:21 UTC, Jack wrote:
> the output is "h" rather "hello". What am I missing?

In the sayHello function, you are converting a pointer to utf16 character into utf8 string, not utf16 string to utf8 string. Convert the C wstring to a D `wstring` first (std.string.fromStringz).

On 09.12.20 21:35, Jack wrote:
> I'm on linux/opensuse, trying to pass a wchar_* from C to D but I'm getting only the first letter of that string. Could someone help figure out why?
> 
> this is the piece of D code:
> 
> extern(C) export
> void sayHello(const (wchar) *s)
[...]
> and below the piece of C code where I call the lib's function, compiled with clang -std=c11 -m64 dll.c -ldl
[...]
>    const wchar_t *s2 = L"hello!";
>    void (*fp)(const wchar_t*) = dlsym(lh, "sayHello");
>    char *de = dlerror();
>    if(de) {
>      fprintf(stderr, "slsym error:%s\n", de);
>      return EXIT_FAILURE;
>    }
>    fp(s2);
> 
> the output is "h" rather "hello". What am I missing?

D's wchar is not C's wchar_t. D's wchar is 16 bits wide. The width of C's wchar_t is implementation-defined. In your case it's probably 32 bits.

Because of that size mismatch, sayHello sees your L"hello!" string as "h\0e\0l\0l\0o\0!\0"w. And the conversion correctly stops at the first null character.

My C isn't very good, but I think char_16t is the correct analog to D's wchar. https://en.cppreference.com/w/c/string/multibyte/char16_t

On Wednesday, 9 December 2020 at 21:21:58 UTC, ag0aep6g wrote:
>
> D's wchar is not C's wchar_t. D's wchar is 16 bits wide. The width of C's wchar_t is implementation-defined. In your case it's probably 32 bits.

In D, C's wchar_t is available as `core.stdc.stddef.wchar_t`.

http://dpldocs.info/experimental-docs/core.stdc.stddef.wchar_t.1.html

On Wednesday, 9 December 2020 at 21:28:04 UTC, Paul Backus wrote:
> On Wednesday, 9 December 2020 at 21:21:58 UTC, ag0aep6g wrote:
>>
>> D's wchar is not C's wchar_t. D's wchar is 16 bits wide. The width of C's wchar_t is implementation-defined. In your case it's probably 32 bits.
>
> In D, C's wchar_t is available as `core.stdc.stddef.wchar_t`.
>
> http://dpldocs.info/experimental-docs/core.stdc.stddef.wchar_t.1.html

Don't use wchar_t in C. It has variable size depending of implementation. On Posix machines (Linux, BSD etc.) it's 32 bit wide UTF-32, on Windows it 16 bit UTF-16.

On Wednesday, 9 December 2020 at 20:35:21 UTC, Jack wrote:
> I'm on linux/opensuse, trying to pass a wchar_* from C to D but I'm getting only the first letter of that string. Could someone help figure out why?
>
> [...]


May be this help to you:

	auto s2 = to!string(s);
to
	auto s2 = fromWChar( s );

wstring fromWChar( const wchar* s )
{
    import std.conv : to;
    return s[ 0 .. wcslen( s ) ].to!wstring;
}


Example: https://run.dlang.io/is/PkCeTZ