A pointer is declared as :
<pointer type=""> *<pointer-name>
In the above declaration :
pointer-type : It specifies the type of pointer. It can be int,char, float etc. This type specifies the type of variable whose address this pointer can store.
pointer-name : It can be any name specified by the user. Professionally, there are some coding styles which every code follows. The pointer names commonly start with ‘p’ or end with ‘ptr’
An example of a pointer declaration can be :
char *chptr;
In the above declaration, ‘char’ signifies the pointer type, chptr is the name of the pointer while the asterisk ‘*’ signifies that ‘chptr’ is a pointer variable.
How to initialize a Pointer?
A pointer is initialized in the following way :
<pointer> =
OR
<pointer declaration="">
<name-of-pointer> =
Note that the type of variable above should be same as the pointer type.(Though this is not a strict rule but for beginners this should be kept in mind).
For example :
char ch = 'c';
char *chptr = &ch; //initialize
OR
char ch = 'c';
char *chptr;
chptr = &ch //initialize
In the code above, we declared a character variable ch which stores the value ‘c’. Now, we declared a character pointer ‘chptr’ and initialized it with the address of variable ‘ch’.
Note that the ‘&’ operator is used to access the address of any type of variable.
How to Use a Pointer?
A pointer can be used in two contexts.
Context 1: For accessing the address of the variable whose memory address the pointer stores.
Again consider the following code :
char ch = 'c';
char *chptr = &ch;
Now, whenever we refer the name ‘chptr’ in the code after the above two lines, then compiler would try to fetch the value contained by this pointer variable, which is the address of the variable (ch) to which the pointer points. i.e. the value given by ‘chptr’ would be equal to ‘&ch’.
For example :
char *ptr = chptr;
The value held by ‘chptr’ (which in this case is the address of the variable ‘ch’) is assigned to the new pointer ‘ptr’.
Context 2: For accessing the value of the variable whose memory address the pointer stores.
Continuing with the piece of code used above :
char ch = 'c';
char t;
char *chptr = &ch;
t = *chptr;
We see that in the last line above, we have used ‘*’ before the name of the pointer. What does this asterisk operator do?
Well, this operator when applied to a pointer variable name(like in the last line above) yields the value of the variable to which this pointer points. Which means, in this case ‘*chptr’ would yield the value kept at address held by chptr. Since ‘chptr’ holds the address of variable ‘ch’ and value of ‘ch’ is ‘c’, so ‘*chptr’ yeilds ‘c’.
When used with pointers, the asterisk ‘*’ operator is also known as ‘value of’ operator.
An Example of C Pointers
Consider the following code :
CODE :
#include <stdio.h>
int main(void)
{
char ch = 'c';
char *chptr = &ch;
int i = 20;
int *intptr = &i;
float f = 1.20000;
float *fptr = &f;
char *ptr = "I am a string";
printf("\n [%c], [%d], [%f], [%c], [%s]\n", *chptr, *intptr, *fptr, *ptr, ptr);
return 0;
}
OUTPUT :
$ ./pointers
[c], [20], [1.200000], [I], [I am a string]
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