Re: Passing string array to C
On Thursday, 10 September 2020 at 15:41:17 UTC, Adam D. Ruppe wrote: On Thursday, 10 September 2020 at 14:31:41 UTC, Andre Pany wrote: [...] You messed up the pointers. [...] Fantastic, thank you so much Adam. Kind regards André
Re: Passing string array to C
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(, ); // 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 = [0];
*c = new size_t();
**c = arr.length;
}
---
Passing string array to C
Hi,
I have this coding. Function `sample` will later be called from C
and should provide access to a string array.
I tried to read the string values after the function call
and I can access the first string, but for the second string,
there is an access violation.
Why does it crash?
Kind regards
André
```
import std;
void main()
{
size_t* i;
const(wchar)* r;
sample(, );
// Try to read the 2 string values
const(wchar) ** r2;
r2 =
auto arr = r2[0..*i];
writeln(to!string(arr[0])); // Works
writeln(to!string(arr[1])); // Fails
}
extern(C) export void sample(const(wchar)** r, size_t** c)
{
string[] arr = ["fooä", "bar"];
auto z = new const(wchar)*[arr.length];
foreach(i, ref p; z)
{
p = toUTF16z(arr[i]);
}
*r = z[0];
*c = new size_t();
**c = arr.length;
}
```
