What is activation record in the context of C and C++?

What does it mean and how important to know about it for a C/C++ programmers?

Is it the same across the platforms, at least conceptually?

I understand it as a block of allocated memory used to store local variable by a function...

I want to know more

An activation record is another name for Stack Frame. It's the data structure that composes a call stack. It is generally composed of:

• Locals to the callee
• Return address to the caller
• Parameters of the callee
• The previous stack pointer (SP) value

The Call Stack is thus composed of any number of activation records that get added to the stack as new subroutines are added, and removed from the stack (usually) as they return.

The actual structure and order of elements is platform and even implementation defined.

For C/C++ programmers, general knowledge of this structure is useful to understand certain implementation features like Calling Conventions and even why do buffer overflows allow 3rd party malicious code to be ran.

A more intimate knowledge will further the concepts above and also allow a programmer to debug their application and read memory dumps even in the absence of a debugger or debugging symbols.

More generally though, a C/C++ programmer can go by a large portion of their hobbyist programming career without even giving the call stack a moments thought.

activation record isn't a concept that is used much in talking about C or C++ langauges themselves. The format of activation records is very much platform specific.

Conceptually, how parameters are passed, the lifetimes of local variables, where functions return to and how the call stack is unwound in response to an expection throw are all important parts of C++ and (with the exception of the latter C). The details of how these are implemented will affect what an activation record looks like for a particular platform but knowledge of this is not usually necessary for writing code in C++ or C.