size of a stack frame always fixed?

Question

During a C++ program execution does stack frame of a particular function always have a constant size or compiler is allowed to do dynamic stack management in some cases, something similar to what alloca() function does? to better describe it I mean offset of a particular local variable or object in the stack frame may change at different executions of function

Answer 1

At least in most typical implementations, the stack frame for a variadic function varies depending on how many variables are passed. For example:

printf("%d", 1); // stack frame contains 1 pointer, one int
printf("%d %d", 1, 2); // stack frame contains one pointer, 2 ints.

Whether the implementation is particularly similar to alloca depends on the implementation though (especially since alloca isn't standard, so how or even if it's implemented may vary).