Passing string array to C

Adam D. Ruppe destructionator at
Thu Sep 10 15:41:17 UTC 2020

On Thursday, 10 September 2020 at 14:31:41 UTC, Andre Pany wrote:
> Why does it crash?

You messed up the pointers.

A string is one star.

An array of strings is two stars.

A pointer to an array of strings is /three/ stars.

import std;

void main()
         size_t* i; // this need not be a pointer either btw
         const(wchar)** r; // array of strings
         sample(&r, &i); // pass pointer to array of strings

         // Try to read the 2 string values
         auto arr = r[0..*i]; // slice array of strings
         writeln(to!string(arr[0])); // Works
         writeln(to!string(arr[1])); // all good

// taking a pointer to an array of strings so 3 stars
extern(C) export void sample(const(wchar)*** r, size_t** c)
         string[] arr = ["foo¤", "bar"];
         auto z = new const(wchar)*[arr.length];
         foreach(i, ref p; z)
                 p = toUTF16z(arr[i]);

         // previously you were sending the first string
         // but not the pointer to the array
         // so then when you index above, arr[1] is bad math
         *r = &z[0];

         *c = new size_t();
         **c = arr.length;

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