digitalmars.D.learn - Interfacing C programs: Pass D string to C function
- Dfr (13/13) Dec 13 2013 Hello
- Ithy (2/15) Dec 13 2013 Try using cast(char*)pattern
- Jonathan M Davis (14/33) Dec 13 2013 The problem is that toStringz returns immutable(char)* (because string i...
- Mike Parker (14/26) Dec 13 2013 Declare the function to like so:
- Jonathan M Davis (6/9) Dec 14 2013 Wait. That was stupid of me. Don't do this. It'll give you a char*, but ...
Hello I trying to write simple wrapper around pcre and have problem passing strings to it. As i understood, the best way is std.string.toStringZ. So, my code look like: string pattern = "...."; pcre_compile2( toStringz(pattern), options, &errcode, &errmsg, &erroffset, cast(char*)null); This gives me error: Error: function pcre_compile2 (char*, int, int*, char**, int*, char*) is not callable using argument types (immutable(char)*, int, int*, char**, int*, char*) Any ideas for better way to do this task ?
Dec 13 2013
On Friday, 13 December 2013 at 08:00:21 UTC, Dfr wrote:Hello I trying to write simple wrapper around pcre and have problem passing strings to it. As i understood, the best way is std.string.toStringZ. So, my code look like: string pattern = "...."; pcre_compile2( toStringz(pattern), options, &errcode, &errmsg, &erroffset, cast(char*)null); This gives me error: Error: function pcre_compile2 (char*, int, int*, char**, int*, char*) is not callable using argument types (immutable(char)*, int, int*, char**, int*, char*) Any ideas for better way to do this task ?Try using cast(char*)pattern
Dec 13 2013
On Friday, December 13, 2013 09:00:20 Dfr wrote:Hello I trying to write simple wrapper around pcre and have problem passing strings to it. As i understood, the best way is std.string.toStringZ. So, my code look like: string pattern = "...."; pcre_compile2( toStringz(pattern), options, &errcode, &errmsg, &erroffset, cast(char*)null); This gives me error: Error: function pcre_compile2 (char*, int, int*, char**, int*, char*) is not callable using argument types (immutable(char)*, int, int*, char**, int*, char*) Any ideas for better way to do this task ?The problem is that toStringz returns immutable(char)* (because string is immutable(string)[]), and your function is taking char*. It will work to pass the result of toStringz to a C function which takes const char* (since immutable will implicitly convert to const), but immutable doesn't implicitly convert to mutable, and casting immutable mutable is almost always a bad idea. The easiest solution would be to use std.utf.toUTFz. e.g. auto cstr = str.toUTFz!(char*)(); or you could do something like auto cstr = str.dup.ptr; In either case, what you're doing is allocating a new char[] which holds the same elements as the original string and getting its ptr property so that you have a char*. - Jonathan M Davis
Dec 13 2013
On 12/13/2013 5:00 PM, Dfr wrote:Hello I trying to write simple wrapper around pcre and have problem passing strings to it. As i understood, the best way is std.string.toStringZ. So, my code look like: string pattern = "...."; pcre_compile2( toStringz(pattern), options, &errcode, &errmsg, &erroffset, cast(char*)null); This gives me error: Error: function pcre_compile2 (char*, int, int*, char**, int*, char*) is not callable using argument types (immutable(char)*, int, int*, char**, int*, char*) Any ideas for better way to do this task ?Declare the function to like so: pcre* pcre_compile2( const(char)*, int, int*, const(char)**, int*, const(ubyte)*); This matches the C declaration according to [1]. immutable args can be passed to const params without seeing your error. Also, note the last paramters. In C, it's declared to be const unsigned char* and the documentation suggest it's intended to be treated as a byte array rather than a string. In that case, const(ubyte)* is the appropriate choice. D declarations of C functions should generally match the C version as closely as possible, including use of const, but with intent taken into account as well (e.g. byte array vs string). [1] https://code.google.com/p/wiimc/source/browse/trunk/libs/pcre/doc/html/pcre_compile2.html?r=423
Dec 13 2013
On Friday, December 13, 2013 01:17:41 Jonathan M Davis wrote:or you could do something like auto cstr = str.dup.ptr;Wait. That was stupid of me. Don't do this. It'll give you a char*, but it won't be null-terminated. If you need char*, then use toUTFz!(char*) - though from what Mike's saying, it sounds like the problem was really your function prototype, which was supposed to take const char* rather than char*. - Jonathan M Davis
Dec 14 2013