Differentiate between declaration and definition in C++.

A declaration introduces a name into the program; a definition provides a unique description of an entity (e.g. type, instance, and function). Declarations can be repeated in a given scope, it introduces a name in a given scope. There must be exactly one definition of every object, function or class used in a C++ program.
A declaration is a definition unless:

• it declares a function without specifying its body,
• it contains an extern specifier and no initializer or function body,
• it is the declaration of a static class data member without a class definition,
• it is a class name definition,
• it is a typedef declaration.

A definition is a declaration unless:

• it defines a static class data member,
• it defines a non-inline member function.

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J.Vijayanand

Difference between declaration and Definition

Declaration
It just indicate the presence of a variable or memberfunction and ends with a semi-colon.

For eg;
int i;-->declaration
add();--->declaration

Definition
It explains the behaviour of the function.If it is a variable it defines its value.

For eg:
int i=2;--->It is definition of a variable
add()--------->Definition
{
int a=2,b=3,c;
c=a+b;
}

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The KINGMAKER
Makes Every Thing Possible

Stuffs (My Blog)

It is really simple to differentiate between a definition and declaration. Good examples you have provided, but a starter might really be confused at the beginning with these terms.

Hai,
The above declaration is correct.

If u cant understand,refer this...

Consider a normal C++ program,

class a
{
add();->Function call
}
void a:add()->Function Definition
{
int c1;->declaration of a variable
cout<<"Enter a1";
cin>>a1;
cout<<"Enter b1";
cin>>b1;
c1=a1+b1;->Definition of a variable
cout<<c1;
}


This is incase of C++ Program..


If u use C,then
void main()
{
int c;->Declaration(Since u didnt assigned value)
c=add();->(Here c is defined(i.e..,Value is assigned through function)
printf("%d",c);
}
int add()
{
int a1,b1,c1;
printf("Enter two numbers");
scanf("%d%d",&a1,&b1);
c1=a1+b1;
return(c1);
}

In the above function the value returned by 'add()' is assigned to 'c'

hi poornima,
i think your definition is too complex.... i think kingmaker has done a clear job, its more than enough to explain the context

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SeeSamJagan
- Sky is not the "LIMIT", Death is not the END, There is still something beyond....

int i;
struct rat { public: int num; int denom; };
int inc(int count) { count = count + 1; }

However the following are only declarations.

extern int i;
struct rat;
extern int inc(int count);

declaration:
its mean the variables or functions have been just created, yet they are not ready for use.
example
int i;
int j;
void doAnything();

Definition

if we need to use those functions and variables we must initialize the variables or build the function. the process to initialize or building functions called definitions.

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Thanks & Regards,
Jegan CBK
"We will either find a way, or make one!”

Thanks guys! I was really looking for this topic on the net, and thank God I found this thread. I had my confusions on how to declare the variables.

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