format specifier %n

The %n Specifier:

The %n format specifier is different from the others. Instead of telling printf( ) to display

something, it causes printf( ) to load the integer variable pointed to by its corresponding argument

with a value equal to the number of characters that have been output. In other words, the value that

corresponds to the %n format specifier must be a pointer to a variable. After the call to printf( ) has

returned, this variable will hold the number of characters output, up to the point at which the %n

was encountered. Examine the next program to understand this somewhat unusual format code:

#include <stdio.h>

int main(void)

{

int count;

printf("this%n is a test\n", &count);

printf("%d", count);

return 0;

output:

this is a test

followed by the number 4.