Malloc and Realloc relation, How does it handle when the required space is not available in memory [duplicate]

Answer 1

RETURN VALUE

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The realloc() function returns a pointer to the newly allocated memory, which is suitably aligned for any kind of variable and may be different from ptr, or NULL if the request fails. If size was equal to 0, either NULL or a pointer suitable to be passed to free() is returned. If realloc() fails the original block is left untouched; it is not freed or moved.