I am a beginner, what is the difference between declaration and definition, thank you

gabriel111

I’m a beginner, I often read the book and say the statement and the definition
It seems that the two are similar. Is there any difference? ? Specifically, thank you

zdl_22

Personal habits are similar, but when using the extern keyword, it is fame rather than definition

hailiu

class a
{
void test(); //declaration
}

void a::test() //define
{
}

The declaration just means that there is such a function, and the definition implements this function!

sevenbox

The declaration of a variable is actually an empty thing. In C++, it is equivalent to an empty pointer. It does not point to anything and has no practical meaning. In fact, it is quite similar to an object. For things in a class, whether it is a function or a variable, it must be accessed through the object, except for the static ones. So, the variable (actual value) in the inner cluster is called through the object of reputation
The definition of a variable is different. It specifies a certain space in the inner cluster, such as 122103, which has a certain practical significance.
The two concepts are related

sevenbox

In fact, in general, the declaration is to let the compiler know that there is this thing, and the definition is to allocate space for this thing

david71

Definition is also a kind of declaration,
But after the definition, the memory of this thing is declared. . .

lplp80131

I suggest you buy a book in C language
Take a look, such as "C Language Reference Manual"

dztgw1974

The statement is that there is this thing, I will not allocate memory space for you
The definition shows that this thing exists, and I allocate the space to you

gabriel111

Haha very specific, thank you everyone for your help