topic Re: Calloc problems in Operating System - HP-UX

Calloc problems

Alex Lavrov — Mon, 19 Jan 2004 10:19:42 GMT

i am doing an allocation of memory like that
: ptr = (char *) calloc (...,size) ;
when it done from main() everything is fine.
but if i call a sub function from the main ,
and allocate the pointer there , when i try to use the variable (ptr[0] = 'a')
i got segmentation fault.
as i mentioned before. it's only happen in a sub-function .
thanks for your help.

Re: Calloc problems

A. Clay Stephenson — Mon, 19 Jan 2004 10:25:20 GMT

I suspect that it a case of the variable becoming undefined upon function exit. Calloc, malloc, ... work just fine inside functions. If you will post a section of your code that illusrates the problem then I suspect the fix will be trivial.

Re: Calloc problems

Adam J Markiewicz — Tue, 20 Jan 2004 14:07:57 GMT

I hope you do not try:

void myalloc( char *ptr )
{
ptr = malloc( 100 );
}

int main( void )
{
char *ptr;
myalloc( ptr );
ptr[ 0 ] = 0;

return 0;
}

Good luck
Adam

Re: Calloc problems

Don Morris_1 — Tue, 20 Jan 2004 15:22:24 GMT

You need to pass the address of ptr from main to the subfunction if you want the updated value back in main. Which also means you need to have the allocation sub-function take char **.

Re: Calloc problems

Kenneth Platz — Fri, 30 Jan 2004 11:23:45 GMT

Your other option is something like this:

char *myfunc() {
char *p;

p=(char *)calloc( size );

/* Do some stuff with p */

return p;
}

int main() {
char *p;

p = myfunc();

/* now you can access p */
}

Hope this helps.