c++ - The differences between initialize, define, declare a variable -

after reading question, know differences between declaration , definition. mean definition equals declaration plus initialization?

declaration

declaration, generally, refers introduction of new name in program. example, can declare new function describing it's "signature":

void xyz(); 

or declare incomplete type:

class klass; struct ztruct; 

and last not least, declare object:

int x; 

it described, in c++ standard, @ §3.1/1 as:

a declaration (clause 7) may introduce 1 or more names translation unit or redeclare names introduced previous declarations.

definition

a definition definition of declared name (or can both definition , declaration). example:

int x; void xyz() {...} class klass {...}; struct ztruct {...}; enum { x, y, z }; 

specifically c++ standard defines it, @ §3.1/1, as:

a declaration definition unless declares function without specifying function’s body (8.4), contains extern specifier (7.1.1) or linkage-specification25 (7.5) , neither initializer nor function- body, declares static data member in class definition (9.2, 9.4), class name declaration (9.1), opaque-enum-declaration (7.2), template-parameter (14.1), parameter-declaration (8.3.5) in function declarator not declarator of function-definition, or typedef declaration (7.1.3), alias-declaration (7.1.3), using-declaration (7.3.3), static_assert-declaration (clause 7), attribute- declaration (clause 7), empty-declaration (clause 7), or using-directive (7.3.4).

initialization

initialization refers "assignment" of value, @ construction time. generic object of type t, it's in form:

t x = i; 

but in c++ can be:

t x(i); 

or even:

t x {i}; 

with c++11.

conclusion

so mean definition equals declaration plus initialization?

it depends. on talking about. if talking object, example:

int x; 

this definition without initialization. following, instead, definition initialization:

int x = 0; 

in context, doesn't make sense talk "initialization", "definition" , "declaration". if talking function, example, initialization not mean much.

so, answer no: definition not automatically mean declaration plus initialization.