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Specifically, is the following legal C++?
class A{};
void foo(A*);
void bar(const A&);
int main(void)
{
foo(&A()); // 1
bar(A()); // 2
}
It appears to work correctly, but that doesn't mean it's necessarily legal. Is it?
Edit - changed A& to const A&
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A mutable object's value can be changed when it is passed to a method. An immutable object's value cannot be changed, even if it is passed a new value. “Passing by value” refers to passing a copy of the value. “Passing by reference” refers to passing the real reference of the variable in memory.
C++ makes both pass by value and pass by reference paradigms possible. You can find two example usages below. Arrays are special constructs, when you pass an array as parameter, a pointer to the address of the first element is passed as value with the type of element in the array.
When an object (or built-in type) is passed by reference to a function, the underlying object is not copied. The function is given the memory address of the object itself. This saves both memory and CPU cycles as no new memory is allocated and no (expensive) copy constructors are being called.
Here are some advantages of passing by reference: No new copy of variable is made, so overhead of copying is saved. This Makes program execute faster specially when passing object of large structs or classes. Array or Object can be pass.
1: Taking the address of a temporary is not allowed. Visual C++ allows it as a language extension (language extensions are on by default).
2: This is perfectly legal.
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