Program crash on array index assignment

Question

I'm having a little problem here. Every time I run the code below, my program just crash.

void Wingcod::push(byte b)
{
    stack[stackp] = b;
    stackp++;
    if(stackp >= stacks)
    {
        stacks += 16;
        try
        {
            realloc(stack,stacks);
        }catch(bad_alloc*)
        {
            cerr << "STACK OVERFLOW";
            exit(1);
        }
    }
}

And stack, stackp and stacks is defined like this:

stacks = 8;
stackp = 0;
stack = new byte[stacks];

And byte is just a unsigned char.

Why not use C++ instead? You can have a handy std::vector<byte> that does exactly what you need. — Kerrek SB
– Kerrek SB, Commented Jan 31, 2012 at 20:39
When i step into the push function, all the variable fields in the debugger turn blank. Weird. — NullData
– NullData, Commented Jan 31, 2012 at 20:47
@Kerrek SB this might sound a bit weird, but i need something more low level than a vector. — NullData
– NullData, Commented Jan 31, 2012 at 20:48

Michael Burr · Accepted Answer · 2012-01-31 20:37:31Z

6

You're not allowed to use realloc() on a pointer that was allocated with new.

Maybe try something like the following instead of realloc():

        byte* tmp = new byte[stacks];
        delete [] stack;
        stack = tmp;

answered Jan 31, 2012 at 20:37

Michael Burr

342k52 gold badges553 silver badges774 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Pubby · Accepted Answer · 2012-01-31 20:37:36Z

4

realloc doesn't throw exceptions as it's not related to new, but C's malloc. It also doesn't set the pointer.

stacks = 8;
stackp = 0;
stack = static_cast<byte*>(malloc(stacks * sizeof(byte)));

void Wingcod::push(byte b)
{
    stack[stackp] = b;
    stackp++;
    if(stackp >= stacks)
    {
        stacks += 16;
        if(!(stack = static_cast<byte*>(realloc(stack,stacks * sizeof(byte))))) {
            cerr << "STACK OVERFLOW";
            exit(1);
        }
    }
}

answered Jan 31, 2012 at 20:37

Pubby

53.3k13 gold badges147 silver badges186 bronze badges

6 Comments

Bo Persson Over a year ago

"Doesn't change the pointer" seems to be an important part of the crash.

NullData Over a year ago

Yeah, it's a solution, but not to my current problem. you see the crash happens at the first line in the function, the first time i run it.

Pubby Over a year ago

@TheBreadCat You can post another question with more code if you think the problem is something else. I was thinking that the calling object (this pointer) might be invalid.

NullData Over a year ago

the wc->push() code is the same as this.push(), it's just a static reference.

Pubby Over a year ago

@TheBreadCat Why is wc a pointer? Are you 100% sure it's not NULL?

|

Dietmar Kühl · Accepted Answer · 2012-01-31 20:38:41Z

4

You cannot use a pointer allocated with new T[n] as an argument for realloc(). The pointers working with realloc() have to come from the malloc() family of functions (malloc(), calloc(), or realloc()). Personally, I wouldn't use any of this but rather use std::vector<T>.

answered Jan 31, 2012 at 20:38

Dietmar Kühl

155k18 gold badges238 silver badges395 bronze badges

Comments

3Pi · Accepted Answer · 2012-01-31 20:39:40Z

0

From here, Realloc only works on a pointer to memory previously assigned by alloc. Try using malloc

answered Jan 31, 2012 at 20:39

3Pi

1,9143 gold badges19 silver badges31 bronze badges

Collectives™ on Stack Overflow

Program crash on array index assignment

4 Answers 4

Comments

6 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

6 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related