Dynamic Memory Allocation

malloc

• Difference between <stdlib.h> and <malloc.h> @ stackoverflow

The <malloc.h> header is deprecated.

• What is the default value after malloc in C? @ stackoverflow

C11, 7.22.3.4 The malloc function

The malloc function allocates space for an object whose size is specified by size 
and whose value is indeterminate.

• Specifically, what's dangerous about casting the result of malloc?

• Do I cast the result of malloc? @ stackoverflow

int *sieve = malloc(sizeof *sieve * length);

• How to find how much space is allocated by a call to malloc()?

It's not in the standard.

But there are platform-specific functions to do this, like _msize or malloc_usable_size.