Learn pointer declarations, pointer to int, function returning pointer, pointer to function, dangling pointer, void pointer with examples.
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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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