Use another language to call a function: Difference between revisions

=={{header|D}}==

This shows how to perform the task on Windows. Elsewhere the procedure is very similar.

First write a D module like this, named "query_func.d":

<lang d>import core.stdc.string;

extern(C) bool query(char *data, size_t *length) pure nothrow {

immutable text = "Here am I";

if (*length < text.length) {

*length = 0; // Also clears length.

return false;

} else {

memcpy(data, text.ptr, text.length);

*length = text.length;

return true;

}

}</lang>

Generate a library file with:

<pre>dmd -lib query_func.d</pre>

This generates a <code>query_func.lib</code> file.

Then create a C file named "mainc.c", given in the task description and here improved a little:

<lang c>#include <stdio.h>

#include <stdbool.h>

extern bool query(char *data, size_t *length);

int main() {

char buffer[1024];

size_t size = sizeof(buffer);

if (query(buffer, &size))

printf("%.*s\n", size, buffer);

else

puts("The call to query has failed.");

return 0;

}</lang>

Then you can compile and link all with the [http://www.digitalmars.com/download/freecompiler.html DMC C compiler](on Linux you can use GCC):

<pre>dmc query_func.lib mainc.c</pre>

It generates the "mainc.exe" binary, that prints the desired output:

<pre>Here am I</pre>