toupperunsigned

toupperunsigned is a non-standard function name used in some codebases to convert an unsigned character or code point to its uppercase form. It is not defined by the C or C++ standard, and its exact behavior depends on the library or project in which it appears. The name typically signals that the input should be treated as unsigned to ensure defined behavior for characters outside the ASCII range.

In its simplest form, a locale-agnostic variant maps ASCII lowercase letters to uppercase: if ch is in the range 'a' to 'z', it returns ch - ('a'-'A'); otherwise it returns ch unchanged. A Unicode-aware variant expands this to map a much larger set of script-specific lowercase letters to their uppercase equivalents, following Unicode case mappings and, if applicable, locale data. Such mappings are usually provided by a dedicated library (for example ICU) or by platform APIs.

Common prototypes include unsigned int toupperunsigned(unsigned int ch) and unsigned char toupperunsigned(unsigned char ch). Using an unsigned input helps avoid undefined behavior when feeding values outside the signed char range. When only ASCII is required, the standard toupper from <ctype.h> suffices, provided the input is cast to unsigned char.

In portable code, developers should document the expected input domain and consider using a Unicode-capable library for non-ASCII text. See also toupper, towupper, and Unicode case mapping resources.