What is the purpose of realloc( ) - peak concepts

The function realloc(ptr,n) uses two arguments.the first argument ptr is a pointer to a block of memory for which the size is to be altered. The second argument n specifies the new size. The size may be increased or decreased. 

If n is greater than the old size and if sufficient space is not available subsequent to the old region, the function realloc( ) may create a new region and all the old data are moved to the new region.

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What is the difference between realloc() and free() - peak concepts

The free subroutine frees a block of memory previously allocated by the malloc subroutine. Undefined results occur if the Pointer parameter is not a valid pointer. If the Pointer parameter is a null value, no action will occur. 

The realloc subroutine changes the size of the block of memory pointed to by the Pointer parameter to the number of bytes specified by the Size parameter and returns a new pointer to the block.

 

The pointer specified by the Pointer parameter must have been created with the malloc, calloc, or realloc subroutines and not been deallocated with the free or realloc subroutines. Undefined results occur if the Pointer parameter is not a valid pointer.

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