Dynamic memory allocation in C is
performed using one of the standard library functions
malloc, calloc or realloc. Dynamically
allocated memory must eventually be freed by calling free. If allocated
memory is not properly freed a memory leak results, which could result
in a program malfunction.
All these functions are in header
file <stdlib.h>.
The malloc() function
This function allocates specified
number of bytes.
It takes a single argument.
It does not initialize the
allocated memory.
It
returns a pointer of type void which can be cast into a pointer of any form.
If space is insufficient, allocation
fails and returns a NULL pointer.
Syntax:
ptr=(cast_type *) malloc(sizeof(type))
Example:
int *ptr;
ptr=(int *) malloc(sizeof(int));
ptr points to memory allotted by malloc() function.
The calloc() function
This function allocates specified
number of bytes.
It takes two arguments.
It initializes each block
allocated memory with a default value of 0.
It
returns a pointer of type void which can be cast into a pointer of any form.
If space is insufficient, allocation
fails and returns a NULL pointer.
Syntax:
ptr=(cast_type *) calloc(n,sizeof(type))
where
n= no of elements
sizeof(type) return no of bytes to be
allotted
Example:
int *ptr;
ptr=(int *) calloc(n,sizeof(int));
ptr points to memory allotted by calloc()
function.
The realloc() function
If someone wants to modify the
memory allotted by malloc() and calloc() functions, this function can be used
to do this.
Syntax:
ptr=(cast_type*) realloc(ptr,sizeof(type))
Example:
int *ptr;
ptr=(int *) malloc(sizeof(int));
ptr=(int*) realloc(ptr,newSize);
The free() function
Memory allotted using malloc() and
calloc() functions should be freed. It
helps to reduce wastage of memory.
Syntax:
free(pointer_variable);
Example:
int *ptr;
ptr=(int *) malloc(sizeof(int));
free(ptr);
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