s in computing architectures are regions of memory where data is added or removed in a last-in-first-out manner. In most moderncomputer systems, each thread has a reserved region of memory referred to as its stack. When a function executes, it may add some of its state data to the top of the stack; when the function exits it is responsible for removing that data from the stack. At a minimum, a thread's stack is used to store the location of function calls in order to allow return statements to return to the correct location, but programmers may further choose to explicitly use the stack. If a region of memory lies on the thread's stack, that memory is said to have been allocated on the stack, i.e. stack-based memory allocation.
Advantages and disadvantages
Because the data is added and removed in a last-in-first-out manner, stack-based memory allocation is very simple and typically faster than heap-based memory allocation. Another feature is that memory on the stack is automatically, and very efficiently, reclaimed when the function exits, which can be convenient for the programmer if the data is no longer required. If however, the data needs to be kept in some form, then it must be copied from the stack before the function exits. Therefore, stack based allocation is suitable for temporary data or data which is no longer required after the creating function exits. A thread's assigned stack size can be as small as only a few bytes on some small CPUs. Allocating more memory on the stack than is available can result in a crash due to stack overflow. This is also why functions that use are usually prevented from being inlined: should such a function be inlined into a loop, the caller would suffer from an unanticipated growth in stack usage, making an overflow much more likely. Stack-based allocation may also cause minor performance problems: it leads to variable-size stack frames, so that both stack and frame pointersneed to be managed. This is usually much less costly than calling and anyway.
System interface
Many Unix-like systems as well as Microsoft Windows implement a function called for dynamically allocating stack memory in a way similar to the heap-based malloc. A compiler typically translates it to inlined instructions manipulating the stack pointer, similar to how variable-length arrays are handled. Although there is no need to explicitly free the memory, there is a risk of undefined behavior due to stack overflow. The function was present on Unix systems as early as 32/V, but is not part of Standard C or any POSIX standard. A safer version of called, which reports errors, exists on Microsoft Windows. It requires the use of. gnulib provides an equivalent interface, albeit instead of throwing an SEH exception on overflow, it delegates to when an overlarge size is detected. A similar feature can be emulated using manual accounting and size-checking, such as in the uses of in glibc. Some processor families, such as the x86, have special instructions for manipulating the stack of the currently executing thread. Other processor families, including PowerPC and MIPS, do not have explicit stack support, but instead rely on convention and delegate stack management to the operating system's application binary interface.
