iscntrlunsigned

iscntrlunsigned is not a standard function in the C library. In practice, it appears as a name used in some codebases to indicate a wrapper or variant of the well-known iscntrl function, with an emphasis on unsigned input. The intended purpose would be to test whether a given character code represents a control character, while ensuring the input is treated as unsigned.

In standard C, iscntrl is declared in ctype.h and takes an int ch. It returns a nonzero value if ch corresponds to a control character in the current locale, and zero otherwise. The value passed to iscntrl should be representable as an unsigned char or be EOF. Because char may be signed on some systems, a common practice is to cast to unsigned char before calling iscntrl to avoid undefined behavior.

If a function named iscntrlunsigned exists, it would typically be a wrapper that enforces unsigned input, such as an unsigned int or unsigned char, and then applies the same control-character classification as iscntrl. A minimal implementation would forward to iscntrl after casting, for example returning iscntrl((unsigned char)ch). However, since iscntrlunsigned is not standardized, its exact signature, range, and locale behavior are not guaranteed and can vary between codebases.

Portability considerations include the fact that control characters are largely defined by the C locale and ASCII subset, so behavior tends to be consistent across platforms, though locale-dependent variants exist for some character classes. When using any nonstandard or wrapper function, it is important to document its contract and ensure consistent behavior across compilers and architectures.

See also: iscntrl, ctype.h, ASCII control characters, character classification.