exern (C) linkage problem

[bearophile]

Lars T. Kyllingstad:
> 2. For D strings in general the \0 must be added, but this is very easy 
> to forget.  Therefore, when passing strings to C functions I always use 
> the std.string.toStringz() function.  It takes a D string, adds a \0 if 
> necessary, and returns a pointer to the first character.
> 
>   string s = getAStringFromSomewhere();
>   dbdefine(toStringz(s));

The C code has to use those string pointers with lot of care.
The D type system can help you remember to use the toStringz, this is just an idea:

import std.string: toStringz;

typedef char* Cstring;
extern(C) Cstring strcmp(Cstring s1, Cstring s2);

Cstring toCString(T)(T[] s) {
    return cast(Cstring)toStringz(s);
}
void main() {
    auto s1 = "abba";
    auto s2 = "red";
    // auto r = strcmp(toCString(s1), s2); // compile error
    auto r = strcmp(toCString(s1), toCString(s2)); // OK
}
Unfortunately Andrei has killed the useful typedef. So you have to use a struct with alias this, that often doesn't work.

Bye,
bearophile