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The C0 and C1 control code or control character sets define control codes for use in text by computer systems that use ASCII and derivatives of ASCII. The codes represent additional information about the text, such as the position of a cursor, an instruction to start a new line, or a message that the text has been received.
There were quite a few control characters defined (33 in ASCII, and the ECMA-48 standard adds 32 more). This was because early terminals had very primitive mechanical or electrical controls that made any kind of state-remembering API quite expensive to implement, thus a different code for each and every function looked like a requirement.
Each string ends at the first occurrence of the zero code unit of the appropriate kind (char or wchar_t).Consequently, a byte string (char*) can contain non-NUL characters in ASCII or any ASCII extension, but not characters in encodings such as UTF-16 (even though a 16-bit code unit might be nonzero, its high or low byte might be zero).
ASCII was incorporated into the Unicode (1991) character set as the first 128 symbols, so the 7-bit ASCII characters have the same numeric codes in both sets. This allows UTF-8 to be backward compatible with 7-bit ASCII, as a UTF-8 file containing only ASCII characters is identical to an ASCII file containing the same sequence of characters.
The \n escape sequence allows for shorter code by specifying the newline in the string literal, and for faster runtime by eliminating the text formatting operation. Also, the compiler can map the escape sequence to a character encoding system other than ASCII and thus make the code more portable.
C character classification is a group of operations in the C standard library that test a character for membership in a particular class of characters; such as alphabetic, control, etc. Both single-byte, and wide characters are supported.
In both ASCII and Unicode, the carriage return is assigned code point 13 (or 0D in hexadecimal); it may also be seen as control+M or ^M. In character and string constants in the C programming language and in many other languages (including representations of regular expressions [2] [3]) influenced by C, \r denotes this character. [4]
For the control-codes outside of the range 1–26, the notation extends to the adjacent, non-alphabetic ASCII characters. Often a control character can be typed on a keyboard by holding down the Ctrl and typing the character shown after the caret.