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C dynamic memory allocation refers to performing manual memory management for dynamic memory allocation in the C programming language via a group of functions in the C standard library, namely , , and . The C++ programming language includes these functions for compatibility with C; however, the operators provide similar functionality and are recommended by that language's authors. Many different implementations of the actual memory allocation mechanism, used by , are available. Their performance varies in both execution time and required memory. ==Rationale== The C programming language manages memory statically, automatically, or dynamically. Static-duration variables are allocated in main memory, usually along with the executable code of the program, and persist for the lifetime of the program; automatic-duration variables are allocated on the stack and come and go as functions are called and return. For static-duration and automatic-duration variables, the size of the allocation must be compile-time constant (except in C99, which allowed variable-length automatic arrays〔(【引用サイトリンク】title=gcc manual )〕). If the required size is not known until run-time (for example, if data of arbitrary size is being read from the user or from a disk file), then using fixed-size data objects is inadequate. The lifetime 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. These limitations are avoided by using dynamic memory allocation in which memory is more explicitly (but more flexibly) managed, typically, by allocating it from the ''free store'' (informally called the "heap"), an area of memory structured for this purpose. In C, the library function malloc is used to allocate a block of memory on the heap. The program accesses this block of memory via a pointer that malloc returns. When the memory is no longer needed, the pointer is passed to free which deallocates the memory so that it can be used for other purposes.Some platforms provide library calls which allow run-time dynamic allocation from the C stack rather than the heap (e.g. alloca()〔〕). This memory is automatically freed when the calling function ends. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「C dynamic memory allocation」の詳細全文を読む スポンサード リンク
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