Editing Printf (section)

{{Short description|C function to format and output text}}
{{More citations needed|date=February 2015}}
{{Use dmy dates|date=January 2021}}
{{Use American English|date=February 2025}}
{{lowercase title|title=printf}}
[[Image:Printf.svg|350px|thumb|alt=Diagram illustrating syntax of printf function. The first argument to the function is a template string, which may contain format specifiers, which are introduced with the percent sign (%) character. Format specifiers instruct printf how to interpret and output values given in the corresponding arguments which follow the format string. printf replaces the format specifiers with the accordingly-interpreted contents of the remaining arguments, and outputs the result.|An example call to the printf function]]

'''printf''' is a [[C standard library]] [[Function (computer programming)|function]] that [[Content format|formats]] [[Plain text|text]] and writes it to [[standard output]]. The function accepts a format [[Null-terminated string|c-string]] [[Parameter (computer programming)|argument]] and a [[variadic|variable]] number of value arguments that the function [[serialization|serializes]] per the format string. Mismatch between the format specifiers and count and [[data type|type]] of values results in [[undefined behavior]] and possibly program [[Crash (computing)|crash]] or other [[Vulnerability (computing)|vulnerability]].

The format string is [[Semantics encoding|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 [[percent sign|{{code|%}}]] 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 programming contexts (i.e. [[programming languages|languages]]) with the same or similar [[Syntax (programming languages)|syntax]] and [[Semantics (computer science)|semantics]].

The [[scanf]] C standard library function complements printf by providing formatted input (a.k.a. [[Lexical analysis|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 [[computer printer|printer]] although the function is not limited to printer output. Today, print refers to output to any text-based environment such as a [[computer terminal|terminal]] or a [[computer file|file]].