What does it mean by C++ runtime?

Question

What are all the activities done by C++ runtime?

Answer 1

It handles startup and shutdown of your application, and the core services it needs to run - things like initialising the stack and static variables, and providing the heap and default memory allocators.

Answer 2

From Wikipedia:

The term C run-time library is used on some platforms to refer to a set of base libraries, which may be distributed in dynamically linkable form with an operating system (with or without header files), or distributed with a C compiler. Another term sometimes used is libc. Not just any library is called the run-time library; run time in this context means the run-time support package associated with a compiler which is understood to make a language complete. The run-time support provides not only the C standard library functions, but possibly other material needed create an environment for the C program, such as initialization prior to the invocation of the main function, or subroutines to provide arithmetic operations missing from the CPU that are needed by code generated by the C compiler.