Both are different, initialization gives value to the variable. *Don't confuse definition with initialization. Declaration is more useful when you want to refer the variable before definition. Int b = 10 // Definition & Initializationĭefinition associates the variable with a type and allocates memory, whereas declaration just specifies the type but doesn't allocate memory. Template class C // declares template class Cĭefinition : extern int a // Declaration Static_assert(X::y = 1, "Oops!") // declares a static_assert which can render the program ill-formed or have no effect like an empty declaration, depending on the result of expr
Using IntVector = std::vector // declares IntVector as an alias to std::vector specific to C++11 - these are not from the standardĮnum X : int // declares X with int as the underlying type
Int g(int lhs, int rhs) // defines N and N::d These are definitions corresponding to the above declarations: int bar It's what the linker needs in order to link references to those entities. These are declarations: extern int bar ĭouble f(int, double) // extern can be omitted for function declarationsĬlass foo // no extern allowed for type declarationsĪ definition actually instantiates/implements this identifier. A declaration is what the compiler needs to accept references to that identifier. A declaration introduces an identifier and describes its type, be it a type, object, or function.
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