Where does the memory come from to initialize a C++ object without the new keyword? -

consider code snippet:

classname* p; p = new classname; 

as understand it, allocating memory heap store *p.

but consider:

classname c; 

question: if not heap, memory c come from?

question: if not heap, memory c come from?

from stack (or in case of global variable or function 'static' variable, statically allocated region exists independently of both heap , stack).

strictly speaking, c++ has no concept of heap or stack (other data structures in standard library, fundamentally different "the" heap , stack prevalent mechanisms used allocation of memory running programs); exact mechanism allocation , management of memory not specified. in practice, there 2 ways program allocate memory @ run time on systems: heap (which built on memory chunks obtained operating system), or stack (the same stack used store return address , save temporary values when functions called).

memory stack allocated when (or before) program begins execution, , needs contiguous. memory heap obtained dynamically , not need contiguous (though in practice heap memory allocated in contiguous chunks).

note first example:

classname* p; p = new classname; 

... embodies 2 allocations: 1 classname object (dynamic storage, allocated on heap) , 1 pointer variable p (automatic storage, allocated on heap).

in practice, local variables not require stack allocation - values can kept in registers (or in cases, storage can optimised away altogether, if value unused or compile-time constant). , theoretically, heap allocations can potentially optimised away.