8/9/2019 Memory Handling in c & c++

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IN

C / C++

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ABSTRACTy Gives knowledge about memory handling functions in

c & c++

y

Includes syntax and examples which makes easier tounderstand and easy to program

y Functions explained are

y C C++

Malloc newCalloc delete

Realloc

Free

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MALLOC

y malloc allocates a block of size bytes from the memoryheap. It allows a program to allocate memory explicitly

as it's needed, and in the exact amounts needed.y The heap is used for dynamic allocation of variable-

sized blocks of memory.

y SYNTAX :

yvoid *malloc(size_t size);

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y Example:y #include y #include y #include y #include

y int main(void)y {y char *str;

y /* allocate memory for string */y if ((str = (char *) malloc(10)) == NULL)y {

y printf("Not enough memory to allocate buffer\n");y exit(1); /* terminate program if out of memory */y }

y /* copy "Hello" into string */y strcpy(str, "Hello");

y

/* display string */y printf("String is %s\n", str);

y /* free memory */y free(str);

y return 0;y }

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CALLOC

y calloc provides access to the C memory heap, which isavailable for dynamic

y allocation of variable-sized blocks of memory.

y SYNTAX :

yvoid *calloc(size_t nitems, size_t size);

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y Example:

y #include y #include y #include

y int main(void)y {y char *str = NULL;

y /* allocate memory for string */y str = (char *) calloc(10, sizeof(char));

y /* copy "Hello" into string */y strcpy(str, "Hello");

y /* display string */

y printf("String is %s\n", str);

y /* free memory */y free(str);

y return 0;

y }

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FREE

y free deallocates a memory block allocated by a

previous call to calloc,y malloc, or realloc.

y SYNTAX :

yvoid free(void *block);

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y free example

y #include

y #include

y #include

y int main(void)

y {

y char *str;

y /* allocate memory for string */

y str = (char *) malloc(10);

y /* copy "Hello" to string */

y strcpy(str, "Hello");

y /* display string */

y printf("String is %s\n", str);

y /* free memory */

y free(str);

y return 0;

y }

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REALLOC

y realloc adjusts the size of the allocated block to size,

copying they contents to a new location if necessary.

y SYNTAX :

y void *realloc(void *block, size_t size);

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y reallocexample

y #include y #include y

#include

y int main(void)y {y char *str;

y /* allocate memory for string */y

str = (char *) malloc(10);

y /* copy "Hello" into string */y strcpy(str, "Hello");

y printf("String is %s\n Address is %p\n", str, str);y str = (char *) realloc(str, 20);

y printf("String is %s\n New address is %p\n", str, str);

y /* free memory */y free(str);

y return 0;y }

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MEMCPY

y these functions copies a block of n bytes from src to

dest.yWith memcpy, if src and dest overlap, the behavior is

undefined.

y SYNTAX :yvoid *memcpy (void *dest, const void *src, size_t n);

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y memcpy example

y #include y #include

y int main(void)y {y char src[] = "******************************";y char dest[] = "abcdefghijlkmnopqrstuvwxyz0123456709";y char *ptr;

y printf("destination before memcpy: %s\n", dest);y ptr = (char *) memcpy(dest, src, strlen(src));y if (ptr)y printf("destination after memcpy: %s\n", dest);y elsey printf("memcpy failed\n");y return 0;y }

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MEMSET

y memset sets the first n bytes of the array s to thecharacter c.

y SYNTAX :

yvoid *memset (void *s, int c, size_t n);

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y Example:

y #include

y #include y #include

y int main(void)

y {

y char buffer[] = "Hello world\n";

y printf("Buffer before memset: %s\n", buffer);

y memset(buffer, '*', strlen(buffer) - 1);

y printf("Buffer after memset: %s\n", buffer);

y return 0;

y

}

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NEW & DELETEy Operators that create and destroy an object

y Syntax:y

= new [ ];y delete ;

y The "new" operator tries to create an object by allocatingy sizeof() bytes in the heap.

y The "delete" operator destroys the object by deallocatingy sizeof() bytes (pointed to by ).

y The storage duration of the new object is from the point of creation untily the operator "delete" deallocates its memory, or until the end of they program.

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y Example:

y name *nameptr; // name is any non-function type

y ...

y if (!(nameptr = new name)) {

y errmsg("Insufficient memory for name");

y exit (1);

y }y // Use *nameptr to initialize new name object

y ...

y delete nameptr; //destroy name; deallocatesizeof(name) bytes