Their performance varies in both execution time and required memory. The pointers on c kenneth reek pdf free download of allocated memory can also cause concern. Neither static- nor automatic-duration memory is adequate for all situations. Automatic-allocated data cannot persist across multiple function calls, while static data persists for the life of the program whether it is needed or not.
In many situations the programmer requires greater flexibility in managing the lifetime of allocated memory. This memory is automatically freed when the calling function ends. However, the size of the array is fixed at compile time. 10 integers, and sets to zero all the bytes within that memory space.
With realloc we can resize the amount of memory a pointer points to. There are advantages and disadvantages to performing such a cast. Under the C standard, the cast is redundant. 32-bit value whereas the actually defined function returns a 64-bit value. The improper use of dynamic memory allocation can frequently be a source of bugs.
Memory allocation is not guaranteed to succeed, and may instead return a null pointer. This wastes memory resources and can lead to allocation failures when these resources are exhausted. OS, and thus dangling pointers may persist for a while and appear to work. The implementation of memory management depends greatly upon operating system and architecture. Some operating systems supply an allocator for malloc, while others supply functions to control certain regions of data.
The allocator will usually expand and contract the heap to fulfill allocation requests. A good allocator will attempt to find an unused area of already allocated memory to use before resorting to expanding the heap. The heap requires enough system memory to fill its entire length, and its base can never change. Thus, any large areas of unused memory are wasted. The heap can get “stuck” in this position if a small used segment exists at the end of the heap, which could waste any magnitude of address space, from a few megabytes to a few hundred. The granularity of this depends on page size. Allocated memory contains an 8 or 16 byte overhead for the size of the chunk and usage flags.