What is the terminology for 1st line of main function?

Question

As shown highlighted in attached snapshot,starting line of main function,i know that it is starting point of main function but what is the proper term for it?can we call it function declaration line?

Answer 1

In simple terms, function declaration means are just declaring the function name, its arguments and its return type.
e.g.

int foo(int x, int y);  ==> Function declaration ends with semicolon ;

Function definition means you are actually defining the functionality. e.g.

int foo(int x, int y){
      return x+y;
}  ==> Function definition enclosed within curly braces { }

And the given main() function is function definition.

In general terms, for conventional purpose may be you can call the first line of a function definition as "function header".

And the entire code within the curly braces { } of the function definition as "function body".

Answer 2

There are two terms in C and C++ that share a common usage, and unfortunately often gets confused with each other. The terms are declaration and definition.

A declaration is telling the compiler that something (a "name") exists, somewhere in the program. A definition is the implementation of the thing that was declared.

For functions, you can have a declaration and definition at the same time.

For example lets say your program have a function named foo, taking one int argument and returning a int value. It can be declared as:

int foo(int arg);

This declaration of the function is also known as declaring the prototype of the function. You need to have this declaration before you call the function, or the compiler won't know that it exist. After the declaration it's possible to call the function, the compiler don't need to see the full implementation of the function, only the declaration.

Then we have the definition, where we implement the function:

int foo(int arg)
{
    return arg * 2;
}

Now lets take another function bar which takes no arguments and returns no value. It has no previous declaration, only a definition:

void bar(void)
{
    // Does something here...
}

But because there's no existing declaration before the definition, the definition is also is the declaration.

---

Also note that there is a big difference between C and C++ when it comes to function declarations.

In C a function taking no arguments must use the argument type void. Not specifying any arguments:

void some_function();

actually declares the function some_function as taking an indeterminate number of arguments of indeterminate type. The C compiler will then fill in the missing arguments details when the first call is made, or when it finds another declaration (or definition) that specifies the arguments.

In C++ such a declaration declares the function as taking no arguments.

This is only one difference between C and C++, and the reason why many of us here don't like questions being tabbed with both languages, or the term "C/C++".

Answer 3

I don't know about C, but here are some snippets from the C++23 draft:

dcl.fct.def/3

Example 1: A simple example of a complete function definition is

int max(int a, int b, int c) {
  int m = (a > b) ? a : b;
  return (m > c) ? m : c;
}

Here int is the decl-specifier-seq; max(int a, int b, int c) is the declarator; { /* ... */ } is the function-body. — end example]

So, in int main() we get that int is the decl-specifier-seq and main() is the declarator.

We also have another example (sorry for only finding examples) dcl.fct/9:

[Example 5: The declaration

int fseek(FILE*, long, int);

declares a function taking three arguments of the specified types, and returning int ([dcl.type]). — end example]

(while not formal), I deduce that the combination of the decl-specifier-seq and the declarator makes the int main() part a declaration.

Answer 4

This line

int main()

in the function definition (that is at the same time a function declaration) is called the function declarator that has the return type (type specifier) int.

That is this code snippet in whole

int main()
{
    //...
}

is a function declaration that introduce the identifier main in the file scope.

Pay attention to that according to the C Standard the function declarator of main that does not accept arguments shall be declared like

int main( void )