Printf

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printf is a C standard library function that formats text and writes it to standard output.

The name, printf is short for print formatted where print refers to output to a printer although the functions are not limited to printer output.

The standard library provides many other similar functions that form a family of printf-like functions. These functions accept a format string parameter and a variable number of value parameters that the function serializes per the format string and writes to an output stream or a string buffer.

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 format string syntax and semantics is the same for all of the functions in the printf-like family.

Mismatch between the format specifiers and count and type of values can cause a crash or vulnerability.

The printf format string is complementary to the scanf format string, which provides formatted input (lexing a.k.a. parsing). Both format strings provide relatively simple functionality compared to other template engines, lexers and parsers.

The formatting design has been copied in other programming languages.