Dynamic Memory Management

1.23 Dynamic Memory Management

In order to make efficient use of memory, it is important for a program to be able to allocate and release blocks of memory dynamically during execution. The functions for dynamic memory management are declared in the header file stdlib.h.

A successful call to one of the memory allocation functions returns the beginning address of a memory block of the requested size. The return value has the type "pointer to void". The program can then use the allocated block in any way desired. When a block of memory is no longer needed, it should be released. All dynamically allocated memory blocks are automatically released when the program exits.

void *malloc ( size_t size  );

Allocates a memory block of size bytes.

void *calloc ( size_t n , size_t size  );

Allocates enough memory to hold an array of n elements, each of which has the size size, and initializes every byte with the value 0.

void *realloc ( void *ptr , size_t n  );

Changes the length of the memory block referenced by ptr to the new length n. If the memory block has to be moved in order to provide the new size, then its current contents are automatically copied to the new location.

void free ( void *ptr  );

Releases the memory block referenced by ptr.

The following example uses malloc to allocate space for an array of 1000 integers:

// Get space for 1000 int values:

int *iArr = (int*)malloc( 1000 * sizeof( int ) );

These functions can be called as often as necessary, and in any order. The pointer argument passed to realloc() and free() must refer to a memory block that has been dynamically allocated, of course.