CODEWITHSUNDEEP
cformat-specifiers
Deepak Tatyaji Ahire
Deepak Tatyaji Ahire

Reputation: 5309

Difference between %d and %.d in C language

I wrote the following code and received a blank output:

int main(){

    int y=0;

    printf("%.d", y);

    return 0;
}

Instead, If I use only %d, I get 0 as the output.

What is the difference between %d and %.d.

Your suggestions are greatly appreciated!

Upvotes: 1

Views: 566

Answers (1)

kaylum
kaylum

Reputation: 14046

A . before the conversion specifier is called the "precision". From the printf man page (emphasis mine):

An optional precision, in the form of a period ('.') followed by an optional decimal digit string. Instead of a decimal digit string one may write "*" or "*m$" (for some decimal integer m) to specify that the precision is given in the next argument, or in the m-th argument, respectively, which must be of type int. If the precision is given as just '.', or the precision is negative, the precision is taken to be zero. This gives the minimum number of digits to appear for d, i, o, u, x, and X conversions,

and

d, i

The int argument is converted to signed decimal notation. The precision, if any, gives the minimum number of digits that must appear; if the converted value requires fewer digits, it is padded on the left with zeros. The default precision is 1. When 0 is printed with an explicit precision 0, the output is empty

So for the example code, %.d means an integer conversion with zero precision. Zero precision means a minimum of zero digits. Since the value to be converted is 0 it is not displayed at all due to the zero precision. In contrast, %d has no explicit precision and hence defaults to a precision of one resulting in printing 0.

Upvotes: 5

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