C dynamic memory allocation

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, mainly malloc, realloc, calloc, aligned_alloc and free.

The C++ programming language includes these functions; however, the operators new and delete provide similar functionality and are recommended by that language's authors. Still, there are several situations in which using new/delete is not applicable, such as garbage collection code or performance-sensitive code, and a combination of malloc and new may be required instead of the higher-level new operator.

Many different implementations of the actual memory allocation mechanism, used by malloc, 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 for the case of variable-length automatic arrays). 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.