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Converting string[] to char**

Suppose I want to forward a set of command line options to a C function, declared as follows, with the D main taking args

extern (C) void init(int argc, char** argv);

void main(string[] args) {
    init(args.length, map!(toStringz)(args));
}

The first parameter is easy enough, but my attempt at applying toStringz to the args array doesn't seem to work. I get cannot implicitly convert expression (map(args)) of type MapResult!(toStringz,string[]) to char**. How do you convert string[] to char** (or even const(char)**).

Solution

  • std.algorithm.map function returns range, which in your case must be changed into array. You can do this using std.array.array. Then you can get array pointer using .ptr. It returns immutable(char**) which is casted into char**:

    extern (C) void init(int argc, char** argv);

void main(string[] args) {
    init(cast(int)args.length, cast(char**)map!(toStringz)(args).array.ptr);
}

    Here's live demo: http://dpaste.dzfl.pl/ff81984c