Re: [Vala] C Integration, it's cool

[Serge Hulne <serge hulne gmail com>]

The following example seems to indicate that it is safe to call an external
function written in C, from a Vala source code, as long as the calling Vala
code knows how to free the memory associated with type of the return value
yielded by the C function.

I am not sure this is true irrespectively of the type of the return value
of the C function.

I guess, this is only true if the type of the return value has a
corresponding type in Vala or if the memory allocated for said value is
freed manually in Vala (which is not vala-like and which is error prone).

Serge.


========================================
#Makefile

all : hello

hello : _hello.c hello.vala
    valac -o hello --save-temps _hello.c hello.vala
========================================


=========================================================
// hello.vala
/////////////////
extern char * hello();

void main(string[] arg) {
     //char* s = hello();                // wrong solution : memory leak (s
is not freed)
     string s = (string)hello();       // correct solution : no memory leak
(s is freed)
     print("s = %s\n", s);
}
==========================================================


=============================================================
// hello.c
////////////
#include <stdlib.h>
#include <string.h>

char * hello(){
    char * a = malloc(sizeof(char)*strlen("hello")+1);
    strcpy(a, "hello");
    return a;
}
==============================================================


serge2 serge2-Macmini:~/development/workspace/vala_test_1/vapi_test$
valgrind ./hello
==30004== Memcheck, a memory error detector
==30004== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==30004== Using Valgrind-3.6.1-Debian and LibVEX; rerun with -h for
copyright info
==30004== Command: ./hello
==30004==
s = hello
==30004==
==30004== HEAP SUMMARY:
==30004==     in use at exit: 45,684 bytes in 361 blocks
==30004==   total heap usage: 426 allocs, 65 frees, 88,577 bytes allocated
==30004==
==30004== LEAK SUMMARY:
==30004==    definitely lost: 0 bytes in 0 blocks
==30004==    indirectly lost: 0 bytes in 0 blocks
==30004==      possibly lost: 3,620 bytes in 66 blocks
==30004==    still reachable: 37,552 bytes in 248 blocks
==30004==         suppressed: 4,512 bytes in 47 blocks
==30004== Rerun with --leak-check=full to see details of leaked memory
==30004==
==30004== For counts of detected and suppressed errors, rerun with: -v
==30004== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 4 from 4)


============================================
for completeness: The temporary C code generated by Vala :
============================================

/* hello.c generated by valac 0.12.0, the Vala compiler
 * generated from hello.vala, do not modify */


#include <glib.h>
#include <glib-object.h>

#define _g_free0(var) (var = (g_free (var), NULL))



gchar* hello (void);
void _vala_main (gchar** arg, int arg_length1);


void _vala_main (gchar** arg, int arg_length1) {
    gchar* _tmp0_ = NULL;
    gchar* s;
    _tmp0_ = hello ();
    s = (gchar*) _tmp0_;
    g_print ("s = %s\n", s);
    _g_free0 (s);
}


int main (int argc, char ** argv) {
    g_type_init ();
    _vala_main (argv, argc);
    return 0;
}
==============================================