The _______ memory allocation function modifies the previous allocated space.

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Accepted Answer

Correct answer: D — ConceptIn C, dynamic memory is handled by a small family of library functions declared in <stdlib.h>, and each of them is defined by the job it performs on the heap: obtaining a fresh block, obtaining a fresh block whose bytes are cleared to zero, changing the size of a block that already exists, or handing a block back to the allocator. A function can act on an allocation made by an earlier call only if its parameter list carries a pointer to that allocation, so the signature rather than the name tells you which job a function does. Applying it hereThe blank asks for the function that modifies the previously allocated space, so it must receive a pointer to a block that already exists together with a new size, and hand back a block of that new size still holding the same data. Comparing the four signatures makes the division of work explicit: Function Signature Job it performs on the heap calloc( ) void *calloc(size_t n, size_t size) Obtains a fresh block large enough for n items of the given size and clears every byte of it to 0. free( ) void free(void *ptr) Hands the block that ptr refers to back to the allocator and ends its lifetime. malloc( ) void *malloc(size_t size) Obtains a fresh block of the requested size and leaves its bytes uninitialised. realloc( ) void *realloc(void *ptr, size_t size) Changes the size of the existing block that ptr refers to, keeping the stored data up to the smaller of the old and the new size. Cross-checkrealloc(ptr, n) may extend the block where it stands when the neighbouring heap space is free; when it cannot, it takes a new block of n bytes, copies the old contents across, releases the old block and returns the new address. A failed call returns a null pointer while the original block stays valid, so the returned value is first stored in a separate pointer, as in q = realloc(p, n), and p is updated only after that pointer has been checked. The remaining boundary case confirms the same job: a resize call whose first argument is a null pointer behaves like a plain allocation of n bytes, so one function covers both starting a block and re-sizing a block that already exists. The new size may be larger or smaller than the old one, and on a shrink the data beyond the new size is discarded. calloc( ) and malloc( ) each begin a new lifetime and are handed sizes rather than a pointer, so neither can touch a block created by an earlier call; free( ) ends a lifetime and hands back no block to work with. ResultThe blank is therefore filled by realloc( ), the C allocation function that modifies the previously allocated space.

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A. calloc( )

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B. free( )

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C. malloc( )

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D. realloc( )

Function	Signature	Job it performs on the heap
`calloc( )`	`void *calloc(size_t n, size_t size)`	Obtains a fresh block large enough for n items of the given size and clears every byte of it to 0.
`free( )`	`void free(void *ptr)`	Hands the block that ptr refers to back to the allocator and ends its lifetime.
`malloc( )`	`void *malloc(size_t size)`	Obtains a fresh block of the requested size and leaves its bytes uninitialised.
`realloc( )`	`void realloc(void ptr, size_t size)`	Changes the size of the existing block that ptr refers to, keeping the stored data up to the smaller of the old and the new size.