How to Specify the Number of Characters to Print from a String using printf()?

Specifying the Number of Characters to Print with printf()

The question arises: is there a mechanism in printf() that allows for specifying the number of characters to print from a string? One might compare this to specifying decimal places in integers. For instance:

printf ("Here are the first 8 chars: %s\n", "A string that is more than 8 chars");

Desirably, this line should output:

Here are the first 8 chars: A string

Solution

There are two primary approaches to achieve this in C.

Method 1: The Basic Approach

printf ("Here are the first 8 chars: %.8s\n", "A string that is more than 8 chars");

Method 2: The Versatile Approach

printf ("Here are the first %d chars: %.*s\n", 8, 8, "A string that is more than 8 chars");

In this approach, the length is provided as an int argument to printf(). The '*' in the format is interpreted as a request to retrieve the length from an argument.

Extended Notation

Another notation can be employed:

printf ("Here are the first 8 chars: %*.*s\n",
        8, 8, "A string that is more than 8 chars");

Analogous to "%8.8s," this notation also enables the specification of minimum and maximum lengths at runtime. This becomes particularly useful in scenarios like:

printf("Data: %*.*s Other info: %d\n", minlen, maxlen, string, info);

The POSIX specification for printf() provides a detailed explanation of these mechanisms.

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