malloc returns a null pointer on failure. So, if what you received isn’t null, then it points to a valid block of memory. Since NULL evaluates to false in an if statement, you can check it in a very straightforward manner: value = malloc(…); if(value) { // value isn’t null } else { // value … Read more
Yes, this is a memory issue: you ran out of memory. I suggest you use Instruments to try to track down any memory leaks.
The POSIX interface of malloc is defined here. If you want to find out how the C library in GNU/Linux (glibc) implements malloc, go and get the source code from http://ftp.gnu.org/gnu/glibc/ or browse the git repository and look at the malloc/malloc.c file. There is also the base documentation of the Memory Allocator by Doug Lea … Read more
You asked 2 questions: for which application the next malloc() call will be faster, #1 or #2? In other words: Does malloc() have an index of allocated locations in memory? You’ve implied that they are the same question, but they are not. The answer to the latter question is YES. As for which will be … Read more
Short answer: Not likely In order for this to work, you absolutely would have to use a 64-bit processor. Secondly, it would depend on the Operating System support for allocating more than 4G of RAM to a single process. In theory, it would be possible, but you would have to read the documentation for the … Read more
You can certainly continue to use p after calling free(p) and nothing will stop you. However the results will be completely undefined and unpredictable. It works by luck only. This is a common programming error called “use after free” which works in many programs for literally years without “problems” — until it causes a problem. … Read more
That’s undefined behavior – never try it. Let’s see what happens when you try to free() an automatic variable. The heap manager will have to deduce how to take ownership of the memory block. To do so it will either have to use some separate structure that lists all allocated blocks and that is very … Read more
A good way is to have the main array beeing alocated ouside the threads. Then you give to each thread the pointer to the part of the main array that should be computed by the thread. The following example is an implementation of a matrix multiplication (similar to dot for 2-D arrays) where: c = … Read more
You can’t execute code outside of functions. The only thing you can do at global scope is declaring variables (and initialize them with compile-time constants). malloc is a function call, so that’s invalid outside a function. If you initialize a global pointer variable with malloc from your main (or any other function really), it will … Read more
This error occurs because some other part of your code has corrupted the heap. We can’t tell you what that error is without seeing the rest of the code. The fact that FINE 7 is not printed tells you that realloc is failing. And that failure must be because buffer is invalid due to a … Read more