What are scanf("%* s ") and scanf("%* d ") format identifiers?

In C programming, the scanf function is a commonly used function for reading and formatting input data from standard input (typically the keyboard). Within this function, specific format specifiers are employed to define the type and structure of input.

The %*s format specifier reads a string but does not store it. This is particularly useful for skipping unnecessary string input. For example, if the user enters '123 abc 456' and you only care about the numbers, you can use %*s to skip 'abc'.

Example Code:

c
#include <stdio.h>

int main() {
    int num1, num2;
    printf("Enter two numbers separated by a non-numeric string: ");
    scanf("%d%*s%d", &num1, &num2);
    printf("Read numbers are: %d and %d\n", num1, num2);
    return 0;
}

The %*d format specifier similarly reads an integer but does not store it. This is useful for skipping integer portions in input. For example, if the user inputs '123 abc 456' and you only care about 'abc', you can use %*d to skip the preceding '123'.

Example Code:

c
#include <stdio.h>

int main() {
    char str[10];
    printf("Enter a number followed by a string: ");
    scanf("%*d%s", str);
    printf("Read string is: %s\n", str);
    return 0;
}

In summary, both %*s and %*d enable skipping unwanted input segments during reading, facilitating more flexible input handling.