c - Is it possible to find the Memory Allocated to the Pointer, without searching for the malloc statement

Question

Suppose I have allocated memory to some pointer in a function foo:

void foo()
{    
    // ...  
    int *ptr = malloc(20*sizeof(int));  

    bar (ptr);
}  

From foo(), I pass this pointer to bar() and let's say from bar() to another function.

Now, at some point of time, I want to check: How much memory was allocated to the pointer.

Is there any possible way, without searching for the statement:

int *ptr = malloc(20*sizeof(int)); 

to figure out how much memory is allocated to the pointer, using GDB?

Thanks.

Answer 1

The answer is: it depends.

Many systems provide msize() [1], malloc_usable_size() [2], or similar function. If you are on such a system, (gdb) print malloc_usable_size(ptr) is all you need.

[1] http://msdn.microsoft.com/en-us/library/z2s077bc(v=vs.80).aspx
[2] http://www.slac.stanford.edu/comp/unix/package/rtems/doc/html/libc/libc.info.malloc.html