Re: what's the right way to get char* from string?

[pineapple via Digitalmars-d-learn]

On Thursday, 5 May 2016 at 07:49:46 UTC, aki wrote:
Hello,
When I need to call C function, often need to
have char* pointer from string.

This might help:

import std.traits : isSomeString;
import std.string : toStringz;

extern (C) int strcmp(char* string1, char* string2);

int strcmpD0(S)(in S lhs, in S rhs) if(is(S == string) || is(S == 
const(char)[])) { // Best
    return strcmp(
        cast(char*) toStringz(lhs),
        cast(char*) toStringz(rhs)
    );
}
int strcmpD1(S)(in S lhs, in S rhs) if(is(S == string) || is(S == 
const(char)[])) { // Works
    return strcmp(
        cast(char*) lhs.ptr,
        cast(char*) rhs.ptr
    );
}

/+
int strcmpD2(S)(in S lhs, in S rhs) if(is(S == string) || is(S == 
const(char)[])) { // Breaks
    return strcmp(
        toStringz(lhs),
        toStringz(rhs)
    );
}
+/

void main(){
    import std.stdio;
    writeln(strcmpD0("foo", "bar")); // Best
    writeln(strcmpD1("foo", "bar")); // Works
    //writeln(strcmpD2("foo", "bar")); // Breaks
}