Cctype
lastmod 2026-11-10created 2020-08-073 edits
cctype is the standard header that wraps C's ctype.h for use in C++, providing functions that classify or convert a single character. It has test functions such as isdigit, isalpha, isspace, and isupper and conversion functions toupper and tolower; they take a character as an int argument and indicate true with a nonzero value. Passing a negative char value as is results in undefined behavior, so the convention is to convert it to unsigned char before passing it.