Learn pointer declarations, pointer to int, function returning pointer, pointer to function, dangling pointer, void pointer with examples. Subscribe here to enable complete access to all technical articles, online tests and projects.
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Pointers, Pointer to integer
A pointer is a variable whose value is the address of another variable.
A pointer to integer holds an address of an integer.
A pointer to integer is declared using the following statement.
int *a; \\a is a pointer to integer.
a is an address where an integer can be stored.
a is the address of the first byte of the integer(4 bytes).
To initialize pointer a we need to assign a to the address of an integer like the follwoing.
int b; \\b is an integer.
a = &b;
An integer pointer can be initialized only with an address of another integer.
Let's understand the application of pointer to an integer using an example program below.
Illustration example
#include "stdio.h"
void PtrToInt(int *);
int main(void)
{
int i = 10;
PtrToInt(&i);
printf("%d\n", i);
}
void PtrToInt(int *a)
{
*a += 1;
}
Output:
$ gcc prog.c
$ ./a.out
11
$
In the above program we have passed a pointer to integer as argument for function PtrToInt. Inside function PtrToInt we increment the value at address a. As we passed the address of integer i while calling the function PtrToInt, the change we make inside the function PtrToInt at address a changes the content of i in main function. So value of i when printed post the PtrToInt function call, it prints the value as 11.
A function returning a pointer to integer
A function returning a pointer to integer returns the address of an integer. You can get the output of a function using a pointer to an integer.
A function returning a pointer to integer is declared in the below statement
int *a(); \\a is a function returning a pointer to integer.
Let's understand the application of a function returning a pointer to an integer using an example program below.
Illustration example
#include "stdio.h"
int *FuncRetPtr(int *);
int main(void)
{
int i = 10;
int *p;
p = FuncRetPtr(&i);
printf("Address at p:%x\n", p);
printf("Content at p:%d\n", *p);
}
int *FuncRetPtr(int *a)
{
*a += 1;
printf("Address at a:%x\n", a);
return a;
}
Output:
$ gcc prog.c
$ ./a.out
Address at a:7ebfa210
Address at p:7ebfa210
Content at p:11
$
In the above program we passed a pointer to an integer to function FuncRetPtr. Inside function FuncRetPtr we increment the content at address a by 1 and then print the address a. As the same address a is returned from the function FuncRetPtr, pointer variable p which captures the output of function FuncRetPtr also prints the same address a. So p is same as address of integer i. So *p prints the value of i incremented by 1.
A pointer to a function
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