islowerint

islowerint is a programming utility used to test whether a given integer represents a lowercase letter in the active character set. It is conceptually analogous to more common character classification functions such as islower, but phrased to emphasize the input as an integer code point rather than a character value in a particular language.

Typically, the function has a signature similar to int islowerint(int ch); it returns a nonzero value when the input corresponds to a lowercase letter, and zero otherwise. The exact interpretation of “lowercase” can be locale-dependent. In ASCII or ASCII-compatible environments, islowerint usually identifies the range corresponding to the lowercase Latin alphabet, namely the codes for 'a' through 'z'. In more general or Unicode-aware implementations, it may classify letters according to the Unicode category Ll (Letter, lowercase) and respect locale settings if locales are enabled.

Implementation details vary by language and library. Some APIs require the input to be a valid unsigned character code or Unicode code point, and passing values outside the valid range can yield undefined behavior or nonzero results depending on the function’s design. To maintain portability, developers should consult the specific documentation for the language and runtime, and consider using locale-aware or Unicode-aware alternatives when working with non-ASCII text.

See also: islower, isupper, isalpha, tolower, toupper, locale.