Tutorial by Examples

It is possible to release dynamically allocated memory by calling free(). int *p = malloc(10 * sizeof *p); /* allocation of memory */ if (p == NULL) { perror("malloc failed"); return -1; } free(p); /* release of memory */ /* note that after free(p), even using the *value...

Standard Allocation The C dynamic memory allocation functions are defined in the <stdlib.h> header. If one wishes to allocate memory space for an object dynamically, the following code can be used: int *p = malloc(10 * sizeof *p); if (p == NULL) { perror("malloc() failed");...

You may need to expand or shrink your pointer storage space after you have allocated memory to it. The void *realloc(void *ptr, size_t size) function deallocates the old object pointed to by ptr and returns a pointer to an object that has the size specified by size. ptr is the pointer to a memory b...

C99 Since C99, C has variable length arrays, VLA, that model arrays with bounds that are only known at initialization time. While you have to be careful not to allocate too large VLA (they might smash your stack), using pointers to VLA and using them in sizeof expressions is fine. double sumAll(si...

realloc is conceptually equivalent to malloc + memcpy + free on the other pointer. If the size of the space requested is zero, the behavior of realloc is implementation-defined. This is similar for all memory allocation functions that receive a size parameter of value 0. Such functions may in fact ...

malloc() often calls underlying operating system functions to obtain pages of memory. But there is nothing special about the function and it can be implemented in straight C by declaring a large static array and allocating from it (there is a slight difficulty in ensuring correct alignment, in pract...

Caveat: alloca is only mentioned here for the sake of completeness. It is entirely non-portable (not covered by any of the common standards) and has a number of potentially dangerous features that make it un-safe for the unaware. Modern C code should replace it with Variable Length Arrays (VLA). Ma...