Thread: Segmentation fault?

Hello all, I'm a beginner in C.

I want to implement a stack data structure.

typedef struct stackNode
{
int value;
struct stackNode *next;
} stackElement;

typedef stackElement *stackPtr;

stackPtr newElement(void)
{
stackPtr element;
element = (stackPtr)malloc(sizeof(stackElement));
element->next = NULL;
return(element);
}

in main function I declare it...

int main(void)
{
stackPtr tmp;
stackPtr stack = NULL;
....

tmp = newElement();
return 0;
}

why every time i try to use newElement()
it gives a runtime error (Segmentation fault,
core dumped)?
And what does the error mean?

Thanks for the help,
Ronald

> 1. first off, the (stackPtr) cast is not necessary (and occasionally wrong) in ANSI-C. You do not need it, if you have #included stdlib.h, and if you haven't, then you'll get a warning.

This is true for most compilers, but some will still give errors about casting from void *; not every compiler out there will allow you to leave the casting off.

> This is true for most compilers, but some will still give errors
> about casting from void *; not every compiler out there will
> allow you to leave the casting off

This is like saying "My program compiles without warnings... if I turn them off for the compiler! That supress errors flag is nice!"

Quzah.

Ok, let me get this straight...

20 seconds ago, on my last post, I was signed in.
Now, I reply to this thread, and suddenly I'm not signed in again?!
Have I ever mentioned how much I hate the timer on this board?
I thought so...

Quzah.

Ok, I have changed my code ...

stackPtr newElement(void)
{
stackPtr element;

element = malloc(sizeof(stackElement));
if ( element == NULL )
{
fprintf( stderr, "Out of memory" );
exit(1);
}

element->next = NULL;
return(element);

}

and alternate it with cast and no-cast with
(stackPtr in front of malloc). But still give
the seg fault error.
Any other explanation?

Thanks for the help
Ronald

I think it's not because of the malloc.
Just declaring
stackPtr tmp;

will give me Seg fault error.

Maybe there's something wrong with my structure?
typedef struct stackNode
{
int value;
struct stackNode *next;
} stackElement;

typedef stackElement *stackPtr;


Thanks for the help,
Ronald

> I think it's not because of the malloc.
> Just declaring
> stackPtr tmp;

The problem is not with this. Just declaring a variable instance does _NOT_ give you a segfault. The error is elsewhere in your program.

Defining a structure also will not give you a segfalt.

Quzah.