Standard library header <cctype>

From cppreference.com

This header was originally in the C standard library as <ctype.h>.

This header is part of the null-terminated byte strings library.

Functions

isalnum	checks if a character is alphanumeric (function)

isalpha	checks if a character is alphabetic (function)

islower	checks if a character is lowercase (function)

isupper	checks if a character is an uppercase character (function)

isdigit	checks if a character is a digit (function)

isxdigit	checks if a character is a hexadecimal character (function)

iscntrl	checks if a character is a control character (function)

isgraph	checks if a character is a graphical character (function)

isspace	checks if a character is a space character (function)

isblank (C++11)	checks if a character is a blank character (function)

isprint	checks if a character is a printing character (function)

ispunct	checks if a character is a punctuation character (function)

tolower	converts a character to lowercase (function)

toupper	converts a character to uppercase (function)

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Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
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Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)