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I understand there are three, not two areas of memory in C++: stack, heap AND the area for static-assigned features. I have two questions
Why is the heap so much slower than the stack? Surely it should just be one extra level of indirection?
Is the area of memory allocated for static “features” (variables, functions, classes) provide faster performance than the heap?
A couple of side notes first. The correct terminology is automatic rather than stack, dynamic rather than heap. The other is that with C++11 there are now four rather than three types of memory. C++11 adds thread local memory to the mix.
Automatic memory is fast because it is implemented using the call stack on most machines. All it takes is to adjust the stack pointer by the right amount and voila! memory is allocated. Dynamic memory requires a whole lot more work underneath the hood. The requisite memory might not be attached to the process, and getting that to happen requires going through the OS. Even if memory is available, the dynamic memory management tools still have to find it and mark it as in use.
Static memory is “allocated” as a part of the compilation and linking process. When you define a static variable in some source file, the compiled code contains special instructions for the linker to reserve space for that variable. The compiler also converts your C/C++ code to machine code. The linker combines all of those different chunks of data and code and resolves addresses to form the executable binary image. When you run your program, that binary image is loaded into (virtual) memory. The memory for that static variable exists as soon as the program starts executing.
As far as performance is concerned, it’s best not to worry too much about performance ahead of time. While static memory is fast, there are lots and lots of drawbacks. The last thing you want to do is to make all of your data static.