Pointer Definition and Declaration
Pointer is a variable, which holds the address of another variable.
Example: if x contains the address of y, then x is said to “pointing to” y.
Declaration:
Like a variable or a constant, we must declare a pointer before we use it to store a variable address.
Pointer is declared with a preceding asterisk (*).
The general form of a pointer variable declaration is: <data-type> * <var-name>;
Where ‘var-name’ is the name of the pointer variable and ‘data-type’ is a regular ‘C’ data type like int, char etc.
Example:
int *ptr; //Here ptr is the integer pointer variable
int ptr; //Here ptr is the normal integer variable
The declaration tells the compiler three things about the variable ‘ptr’
-Te asterisk (*) tells that the variable ‘ptr’ is a pointer variable.
-‘ptr’ needs a memory location.
-‘ptr’ points to a variable of type ‘data-type’.
Example:
int i=5;
int *ptr; //declare a pointer variable
ptr=&i; //store address of ‘i’ in ‘ptr’
printf(“*ptr=%d\n”,*ptr); //refer to reference of ‘ptr’
Here, ptr is a variable storing an address but not storing the actual value of ‘i’
Pointer Operators
There are two operators that are used with pointers namely, address-of-operator(&) and indirection/de-reference operator(*).
Address-of operator(&): it returns the address of the variable instead of stored value.
“&” is used on a variable (int, char, double and array element) to get the address:
Example: ptr = &j;
Address
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Content
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Address
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Content
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Address
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1000
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i:
40
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1001
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j:
33
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1002
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1004
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ptr:
1001
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1005
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1006
|
“&” cannot be used on a constant, array name, register variable and expressions:
Example:
ip1 =&”abcdef”; //incorrect
ip1 = “abcdef”; //correct
indirection/De-reference operator (*): It indicates that ptr is a pointer to type int and not a normal variable of type int.
‘*’ is used on a pointer to access the variable it points to.
Example:
int x=1, y ={2,3};
int *ip1, *ip2, *ip3;
ip1 = &x;
*ip1 =0; //x=0
printf(“%d\t%d\n”, x,y[0]);
ip2 =&y[0];
*ip2 = 1; //y[0] = 1;
“* pointer” has a data type which is the same as that of the variable the pointer points to.
int *a;
every pointer points to a specific data type except void *;
void pointer (void *) is used to hold the address of any data type.
Example:
ptr = &j;
*ptr = 99;
Refer to the content of the referee
Address
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Content
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Address
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Content
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1000
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i: 40
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1001
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j: 99
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1004
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ptr: 1001
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1005
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