[mercury-users] Filling Mercury strings in C

[Peter Ross]

On Tue, Mar 25, 2003 at 01:18:36PM +0100, Petr Nemec wrote:
> Hello people,
>  does anybody know (sure he does :),how to fill the Mercury strings
> in C properly? I use the attached code to read a line and to destroy
> ending \n in C. But it seems the memory for the allocated strings is
> not being freed at all during the computation. Do I allocate right :)
> ?

You need to use MR_NEW(<type to allocate>) or
MR_NEW_ARRAY(<type>, <num>) to allocate your memory on the GC'd heap.

So the line
    sDynamic = malloc(nLength);
should be
    sDynamic = MR_NEW_ARRAY(MR_Char, nlength);

> :- pred creadstring(int,string).
> :- mode creadstring(in,out) is semidet.
> 
> :-pragma
> c_code(creadstring(Pointer::in,String::out),[will_not_call_mercury],
> "
> char buffer[MAX_LINE];
> char* sDynamic;
> 
> if(fgets(buffer,MAX_LINE,(FILE*)Pointer) != NULL)
> {
>  nLength = strlen(buffer);
>  buffer[nLength-1] = '\\0';
>  sDynamic = malloc(nLength);
>  strcpy(sDynamic,buffer);
>  String = sDynamic;
>   SUCCESS_INDICATOR = 1;
> }
> else
>   SUCCESS_INDICATOR = 0;
> ").
> 
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