Nonprintflike

Nonprintflike is a term used in programming discussions to describe APIs that are structurally similar to printf-style interfaces but do not perform standard printf-style output. In such APIs, a function may take a format string and arguments, but instead of printing, it may validate the format, build and return a formatted result, or apply the formatting to a data structure or non-output target (for example, a log entry, a GUI element, or a localization string). The term is informal and context-dependent; it is not a formal language feature in mainstream languages, and not all projects use the label consistently.

Common characteristics include a separation between formatting syntax and the output destination, potential differences in argument handling or type safety, and a focus on correctness checks or non-output use cases. Nonprintflike functions may still use a format-like syntax, but they interpret placeholders for purposes other than emitting characters to a console or file. They may also forego variadic argument lists in favor of typed parameters or data structures.

Examples of nonprintflike usage can include: a function that validates a format string and returns error information without producing output; a templating utility that uses printf-like placeholders to generate UI strings with proper escaping; or a formatting API that returns a string rather than writing directly to an output stream. In compiler or library design, distinguishing nonprintflike from printf-like APIs helps clarify intended side effects and safety guarantees.

See also: printf, format attribute, variadic functions, string templating.