Understanding the basics

Language Environment provides the following types of storage:

Stack storage is automatically created by Language Environment and is used for routine linkage and automatic storage. Refer to Stack storage overview for more information.
Heap storage is dynamically allocated at a routine's first request for storage that has a lifetime not related to the execution of the current routine. Refer to Heap storage overview for more information.

In addition to heap and stack storage, Language Environment® provides a function that allows AMODE 64 applications to manipulate memory objects. The __moservices() function allows an application to:

Create a memory object that will be associated with the current Language Environment enclave. The user can request certain attributes to be applied to the memory object, such as the dump priority, and the size of the page frames to be used when backing it.
Free a memory object that was created using a previous __moservices() call
Specify a shared memory dump priority to be used when allocating shared memory

For more information about __moservices(), refer to z/OS XL C/C++ Runtime Library Reference.

Table 1 summarizes the ways in which Language Environment-conforming languages use stack and heap storage. The remainder of this section further discusses stack and heap storage concepts and terminology.

Table 1. Usage of stack and heap storage by Language Environment-conforming languages
Language	Stack	Heap
C or C++	Automatic variables Library routines	Variables allocated by: `malloc()` function `__malloc31()` function `__malloc24()` function `calloc()` function `realloc()` function Static external (RENT)