C-binding external array.

[Ali Çehreli via Digitalmars-d-learn]

On 08/09/2016 11:46 AM, ciechowoj wrote:
 > On Tuesday, 9 August 2016 at 15:41:08 UTC, Steven Schveighoffer wrote:
 >> @property int* tabp() { return tab.ptr; }
 >>
 >> tabp[elem];
 >
 > This is nice. The best would be to have it with the same name as
 > original symbol, but I can't imagine how it could be done.

Well, C's array symbol is used as a pointer to the first element and D 
allows array indexing for pointers as well.

Here is the C code:

// c.c
#include "stdio.h"

int tab[64];

int *get() {
     return tab;    // or &tab[0]
}

void info() {
     printf("%p\n", tab);
}

void write_at(int i, int value) {
     tab[i] = value;
}

int read_at(int i) {
     return tab[i];
}

The D code uses the array as a pointer and then makes a slice at the 
very end:

// d.d
import std.stdio;

extern (C) {
     int *get();
     void info();
     void write_at(int i, int value);
     int read_at(int i);
}

void main() {
     int *tab = get();
     info();
     writefln("0x%s", tab);

     // make sure we can see what C writes
     write_at(7, 77);
     assert(tab[7] == 77);

     // make sure C can read what we write
     tab[42] = 42;
     assert(read_at(42) == 42);

     // If you know the size, use as a D array
     int[] tab_D = tab[0..64];
     writeln(tab_D);
}

Ali