snprintf() in C

In C, snprintf() function is a standard library function that is used to print the specified string till a specified length in the specified format. It is defined in the <stdio.h> header file.

In this article, we will learn about snprintf() function in C and how to use it in our program.

Syntax

Parameters

• str: It is a pointer to the buffer.
• size: It is the maximum number of bytes (characters) that will be written to the buffer.
• format: C string that contains a format string that follows the same specifications as format in printf.
• (...): The optional ( …) arguments are just the string formats like (“%d”, myint) as seen in printf.

Return Value

• The number of characters that would have been written on the buffer, if 'n' had been sufficiently large.
• If an encoding error occurs, a negative number is returned.

Examples of snprintf()

Example 1:

Below is an example to illustrate the working of snprintf() method:

Writing geeksforgeeks onto buffer with capacity 6
String written on buffer = geeks
Value returned by snprintf() method = 14

Example 2:

The number of bytes printed to 'buffer' (excluding the null terminator) is 45
Joined string:
The quick brown fox jumped over the lazy dog.

Characteristics of snprintf() Method

• The snprintf() function formats and stores a series of characters and values in the array buffer. 
• The snprintf() function accepts an argument 'n', which indicates the maximum number of characters (including at the end of null character) to be written to buffer. 
• The snprintf() function is used to redirect the output of  printf() function onto a buffer. 
• The snprintf() also returns the number characters that were supposed to be written onto the buffer (excluding the null terminator), irrespective of the value of 'n' passed.
• So, only when the returned value is non-negative and less than 'n', the string has been completely written as expected.