12.3: Stack Dynamic Local Variables

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In a high-level language, non-static local variables declared in a function are stack dynamic local variables by default. Some C++ texts refer to such variables as automatics. This means that the local variables are created by allocating space on the stack and assigning these stack locations to the variables. When the function completes, the space is recovered and reused for other purposes. This requires a small amount of additional run-time overhead, but makes a more efficient overall use of memory. If a function with a large number of local variables is never called, the memory for the local variables is never allocated. This helps reduce the overall memory footprint of the program which generally helps the overall performance of the program.

In contrast, statically declared variables are assigned memory locations for the entire execution of the program. This uses memory even if the associated function is not being executed. However, no additional run-time overhead is required to allocate the space since the space allocation has already been performed (when the program was initially loaded into memory).