What is the difference between a defining instance and an external declaration?

A defining instance is a declaration of a variable or function that actually defines and allocates space for that variable or function. In the case of a variable, the defining instance may also supply an initial value, using an initializer in the declaration. In the case of a function, the defining instance supplies the body of the function.

An external declaration is a declaration which mentions the name and type of a variable or function which is defined elsewhere. An external declaration does not allocate space; it cannot supply the initial value of a variable; it does not need to supply the size of an array; it does not supply the body of a function. (In the case of functions, however, an external declaration may include argument type information; in this case it is an external prototype declaration.)

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More Useful Topics...

 

History Of C..

In the beginning was Charles Babbage and his Analytical Engine, a machine
he built in 1822 that could be programmed to carry out different computations.
Move forward more than 100 years, where the U.S. government in
1942 used concepts from Babbage’s engine to create the ENIAC, the first
modern computer.
Meanwhile, over at the AT&T Bell Labs, in 1972 Dennis Ritchie was working
with two languages: B (for Bell) and BCPL (Basic Combined Programming
Language). Inspired by Pascal, Mr. Ritchie developed the C programming
language.

My 1st Program...


#include
#include
void main ()
{
clrscr ();
printf ("\n\n\n\n");
printf ("\t\t\t*******Pankaj *******\n");
printf ("\t\t\t********************************\n");
printf ("\t\t\t\"Life is Good...\"\n");
printf ("\t\t\t********************************");
getch ();
}

Next Step...


#include
#include

void main ()
{
clrscr ();
printf ("\n\n\n\n\n\n\n\n");
printf ("\t\t\t --------------------------- \n\n");

printf ("\t\t\t | IGCT, Info Computers, INDIA | \n\n");
printf ("\t\t\t --------------------------- ");

getch ();

}

Hits!!!