Efficient C++ Performance Programming Techniques

Pass by Value

When passing an object by value, the initialization of the formal parameter with the actual parameter is equivalent to the following form [ES90]:

T formalArg = actualArg;

where T is the class type. Suppose g() is some function expecting a T argument when invoked:

void g (T formalArg)
{
    ...
}

A typical invocation of g() may look like:

T t;
g(t);

The activation record for g() has a place holder on the stack for its local argument formalArg. The compiler must copy the content of object t into g()'s formalArg on the stack. One popular technique of doing this will generate a temporary [Lip96I].

The compiler will create a temporary object of type T and copy-construct it using t as an input argument. This temporary will then be passed ...