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In computer science, an in-tree or parent pointer tree is an N-ary tree data structure in which each node has a pointer to its parent node, but no pointers to child nodes. When used to implement a set of stacks , the structure is called a spaghetti stack , cactus stack or saguaro stack (after the saguaro , a kind of cactus). [ 1 ]
A typical stack, storing local data and call information for nested procedure calls (not necessarily nested procedures). This stack grows downward from its origin. The stack pointer points to the current topmost datum on the stack. A push operation decrements the pointer and copies the data to the stack; a pop operation copies data from the ...
If a pop operation on the stack causes the stack pointer to move past the origin of the stack, a stack underflow occurs. If a push operation causes the stack pointer to increment or decrement beyond the maximum extent of the stack, a stack overflow occurs. Some environments that rely heavily on stacks may provide additional operations, for example:
In 8086, the main stack register is called "stack pointer" (SP). The stack segment register (SS) is usually used to store information about the memory segment that stores the call stack of currently executed program. SP points to current stack top. By default, the stack grows downward in memory, so newer values are placed at lower memory addresses.
In C++, a class can overload all of the pointer operations, so an iterator can be implemented that acts more or less like a pointer, complete with dereference, increment, and decrement. This has the advantage that C++ algorithms such as std::sort can immediately be applied to plain old memory buffers, and that there is no new syntax to learn ...
The stack segment contains the call stack, a LIFO structure, typically located in the higher parts of memory. A "stack pointer" register tracks the top of the stack; it is adjusted each time a value is "pushed" onto the stack. The set of values pushed for one function call is termed a "stack frame". A stack frame consists at minimum of a return ...
To emphasize the effect of a statement, a comment is often used showing the top of the stack before and after the statement; this is known as the stack effect diagram. Some stack-oriented languages may use multiple stacks for different purposes; for example, PostScript uses separate stacks for variables, dictionaries, procedures, some typical ...
Pointer formats are known as near, far, or huge. Near pointers are 16-bit offsets within the reference segment, i.e. DS for data and CS for code. They are the fastest pointers, but are limited to point to 64 KB of memory (to the associated segment of the data type). Near pointers can be held in registers (typically SI and DI).