Use of %n format specifier in C

Question

What does the format specifier %n of printf function do?

Answer 1

Unlike other specifiers, the argument associated with the %n specifier will be treated as a int* and filled with the number of total characters printed at that point in the printf.
See the below example.

#include<stdio.h>
int main()
{
  int count;
  printf("good %n morning ", &count);
  printf("%d", count);

  return 0;
}

The above program prints good morning 5.
The first printf() prints “good morning”.
The second printf() prints 5 as there are 5 characters printed before %n in the first printf.

Comments

Ranjith.. thanks for your answer.. but I have one more doubt.. like could you please explain me behaviour of %n in scanf..

---

The %n specifier instructs scanf() to store the number of characters read from the input so far by this scanf call. No input is consumed, and the return value is not incremented.

Answer 2

%n will be used to write number of characters are printed before %n format specified in printf
for exp:

#include <stdio.h>

int main()
{
    int val = 0;

    printf("count %n written count to val\n", &val);

    printf("val = %d\n", val);

    return 0;

}

output :

 countwritten count to val
 val = 5  (before %n number of characters were 5 i.e count )

Answer 3

It stores the number of character printed so far.

int n;
printf("Hemant %n Patel", &n);
printf("%d", n);

Output:
Hemant Patel
7

Answer 4

It doesn't print anything. It is used to figure out how many characters got printed before %n appeared in the format string.

Use of %n with printf() and scanf():

int main()
{
    int temp = 0;
    int x = -1;
    printf("Testing %n\n",  &temp);
    //It will store the no of char got printed i.e Testing + one space char total 8 to "temp"

    scanf("%n", &x);  //Here not a single char is given .. to it store 0 to x
    printf("x = %d\n", x);

    scanf("%d%n", &temp, &x); // Here it will wait for user to give input and store its no of digit to x.
    printf("x = %d\n", x);

    return 0;
 }

Answer 5

In Case of printf- filled with the number of total characters printed at that point in the printf...
And in case of scanf -new line from previous input is being considered for consecutive scanfs

For eg:

 #include < stdio.h >
int main()
{
   int temp = 0;
   int x = -1;
   printf("Testing %n\n",  &temp);
   //It will store the no of char got printed i.e Testing + one space char total 8 to "temp"

   scanf("%d%n", &temp,&x);  //Here not a single char is given .. to it store 0 to x
   printf("x = %d\n", x);

   scanf("%d%n", &temp, &x); // Here it will wait for user to give input and store its no of digit to x.
   printf("x = %d\n", x);

   scanf("%d%n", &temp,&x);  //Here not a single char is given .. to it store 0 to x
   printf("x = %d\n", x);
   return 0;
} 

o/p:
Testing 
12
x = 2
123
x = 4
1234
x = 5