printf is a C standard library function that formats text and writes it to standard output. The function accepts a format c-string argument and a variable number of value arguments that the function serializes per the format string. Mismatch between the format specifiers and count and type of values results in undefined behavior and possibly program crash or other vulnerability.

The format string is encoded as a template language consisting of verbatim text and format specifiers that each specify how to serialize a value. As the format string is processed left-to-right, a subsequent value is used for each format specifier found. A format specifier starts with a % character and has one or more following characters that specify how to serialize a value.

The standard library provides other, similar functions that form a family of printf-like functions. The functions share the same formatting capabilities but provide different behavior such as output to a different destination or safety measures that limit exposure to vulnerabilities. Functions of the printf-family have been implemented in other computer programming contexts (i.e., programming languages) with the same or similar syntax and semantics.

The scanf() C standard library function complements printf by providing formatted input (a.k.a. lexing, a.k.a. parsing) via a similar format string syntax.

The name, printf, is short for print formatted where print refers to output to a printer although the function is not limited to printer output. Today, print refers to output to any text-based environment such as a terminal or a file.

Early programming languages like Fortran used special statements with different syntax from other calculations to build formatting descriptions. In this example, the format is specified on line 601, and the PRINT command refers to it by line number:

Hereby:

An output with input arguments 100, 200, and 1500.25 might look like this: