Escape sequences
Escape sequences are used to represent certain special characters within string literals and character literals.
The following escape sequences are available:
| Escape sequence | Description | Representation | ||||||
|---|---|---|---|---|---|---|---|---|
| Simple escape sequences | ||||||||
| ' | single quote | byte 0x27 in ASCII encoding | ||||||
| " | double quote | byte 0x22 in ASCII encoding | ||||||
| ? | question mark | byte 0x3f in ASCII encoding | ||||||
| \ | backslash | byte 0x5c in ASCII encoding | ||||||
| \a | audible bell | byte 0x07 in ASCII encoding | ||||||
| \b | backspace | byte 0x08 in ASCII encoding | ||||||
| \f | form feed - new page | byte 0x0c in ASCII encoding | ||||||
| \n | line feed - new line | byte 0x0a in ASCII encoding | ||||||
| \r | carriage return | byte 0x0d in ASCII encoding | ||||||
| \t | horisontal tab | byte 0x09 in ASCII encoding | ||||||
| \v | vertical tab | byte 0x0b in ASCII encoding | ||||||
| Numeric escape sequences | ||||||||
| arbitrary octal value |
| ||||||
| arbitrary hexadecimal value | code unit n... (arbitrary number of hexadecimal digits) | ||||||
| Conditional escape sequences[1] | ||||||||
| \c | Implementation-defined | Implementation-defined | ||||||
| Universal character names | ||||||||
| arbitrary Unicode value; may result in several code units |
| ||||||
| \N{NAME} (od C++23) | arbitrary Unicode character | character named by NAME (see below) |
- ↑ Conditional escape sequences are conditionally-supported.
The character c in each conditional escape sequence is a member of basic source character set (do C++23)basic character set (od C++23)
that is not the character following the
\in any other escape sequence.
Range of universal character names
If a universal character name corresponds to a code point that is not 0x24 ($), 0x40 (@), nor 0x60 (`) and less than 0xA0, the program is ill-formed. In other words, members of basic source character set and control characters (in ranges 0x0-0x1F and 0x7F-0x9F) cannot be expressed in universal character names.
(do C++11)If a universal character name corresponding to a code point of a member of basic source character set or control characters appear outside a character or string literal, the program is ill-formed.
If a universal character name corresponds surrogate code point (the range 0xD800-0xDFFF, inclusive), the program is ill-formed.
If a universal character name used in a UTF-16/32 string literal does not correspond to a code point in ISO/IEC 10646 (the range 0x0-0x10FFFF, inclusive), the program is ill-formed.
(od C++11) (do C++20)If a universal character name corresponding to a code point of a member of basic source character set or control characters appear outside a character or string literal, the program is ill-formed.
If a universal character name does not correspond to a code point in ISO/IEC 10646 (the range 0x0-0x10FFFF, inclusive) or corresponds to a surrogate code point (the range 0xD800-0xDFFF, inclusive), the program is ill-formed.
(od C++20) (do C++23)If a universal character name corresponding to a scalar value of a character in the basic character set or a control character appear outside a character or string literal, the program is ill-formed.
If a universal character name does not correspond to a scalar value of a character in the translation character set, the program is ill-formed.
(od C++23)Named universal character escapes
| \N | | { | n-char-sequence | } | |
| pub | n-char-sequence | one or more n-chars |
| pub | n-char | a character from the translation character set, except the right curly bracket } or new-line character |
A universal character name of the syntax above is a named universal character. It designates the corresponding character in the Unicode Standard (chapter 4.8 Name) if the n-char-sequence is equal to its character name or to one of its character name aliases of type “control”, “correction”, or “alternate”; otherwise, the program is ill-formed.
These aliases are listed in the Unicode Character Database’s NameAliases.txt. None of these names or aliases have leading or trailing spaces.
A valid n-char-sequence must contain only uppercase Latin letters A through Z, digits, space, and hyphen-minus. Other characters never occur in a Unicode character name, and thus their appearance in a n-char-sequence always renders the program ill-formed.
(od C++23)Notes
\0 is the most commonly used octal escape sequence, because it represents the terminating null character in null-terminated strings.
The new-line character \n has special meaning when used in text mode I/O: it is converted to the OS-specific newline representation, usually a byte or byte sequence. Some systems mark their lines with length fields instead.
Octal escape sequences have a limit of three octal digits, but terminate at the first character that is not a valid octal digit if encountered sooner.
Hexadecimal escape sequences have no length limit and terminate at the first character that is not a valid hexadecimal digit. If the value represented by a single hexadecimal escape sequence does not fit the range of values represented by the character type used in this string literal (char, char8_t (od C++20), char16_t, char32_t (od C++11), or wchar_t), the result is unspecified.
A universal character name in a narrow string literal or a 16-bit string literal may map to more than one code unit, e.g. \U0001f34c is 4 char code units in UTF-8 (\xF0\x9F\x8D\x8C) and 2 char16_t code units in UTF-16 (\xD83C\xDF4C).
The question mark escape sequence \? is used to prevent trigraphs from being interpreted inside string literals: a string such as
| Feature-test macro | Value | Std | Comment |
|---|---|---|---|
| __cpp_named_character_escapes | 202207L | (C++23) | Named universal character escapes |
Example
#include <iostream>
int main()
{
std::cout << "This\nis\na\ntest\n\n";
std::cout << "She said, \"Sells she seashells on the seashore?\"\n";
}
This
is
a
test
She said, "Sells she seashells on the seashore?"
Defect Reports
The following behavior-changing defect reports were applied retroactively to previously published
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| CWG 505 | (C++98) | the behavior was undefined if the character following a backslash was not one of those specified in the table | made conditionally supported (semantic is implementation-defined) |