C malloc()The name "malloc" stands for memory allocation.
The malloc() function reserves a block of memory of the specified number of bytes. And, it returns a pointer of void which can be casted into pointers of any form. Syntax of malloc()
ptr = (castType*) malloc(size);
Example
ptr = (float*) malloc(100 * sizeof(float));
The above statement allocates 400 bytes of memory. It's because the size of float is 4 bytes. And, the pointer ptr holds the address of the first byte in the allocated memory.
The expression results in a NULL pointer if the memory cannot be allocated. C calloc()
The name "calloc" stands for contiguous allocation.
The malloc() function allocates memory and leaves the memory uninitialized, whereas the calloc() function allocates memory and initializes all bits to zero.
Syntax of calloc()
ptr = (castType*)calloc(n, size);
Example:
ptr = (float*) calloc(25, sizeof(float));
The above statement allocates contiguous space in memory for 25 elements of type float.
C free()
Dynamically allocated memory created with either calloc() or malloc() doesn't get freed on their own. You must explicitly use free() to release the space.
Syntax of free()
free(ptr);
This statement frees the space allocated in the memory pointed by ptr.
C realloc()
If the dynamically allocated memory is insufficient or more than required, you can change the size of previously allocated memory using the realloc() function.
Syntax of realloc()
ptr = realloc(ptr, x);
Here, ptr is reallocated with a new size x.
