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 |
horizontal tab | byte 0x09 in ASCII encoding |
\v |
vertical tab | byte 0x0b in ASCII encoding |
| Numeric escape sequences | ||
\nnn |
arbitrary octal value | byte nnn |
\xnn |
arbitrary hexadecimal value | byte nn |
| Conditional escape sequences[1] | ||
\c |
Implementation-defined | Implementation-defined |
| Universal character names | ||
\unnnn |
arbitrary Unicode value; may result in several code units |
code point U+nnnn |
\Unnnnnnnn |
arbitrary Unicode value; may result in several code units |
code point U+nnnnnnnn |
- Conditional escape sequences are conditionally-supported. The character
cin each conditional escape sequence is a member of basic source character set (until C++23)basic character set (since 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 ( |
(until 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. |
(since C++11) (until 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. |
(since C++20) (until 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. |
(since 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 (since C++20), char16_t, char32_t (since 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. |
(since C++11) |
The question mark escape sequence \? is used to prevent trigraphs from being interpreted inside string literals: a string such as "??/" is compiled as "\", but if the second question mark is escaped, as in "?\?/", it becomes "??/". As trigraphs have been removed from C++, the question mark escape sequence is no longer necessary. It is preserved for compatibility with C++14 (and former revisions) and C. (since C++17).
Example
#include <iostream>
int main()
{
std::cout << "This\nis\na\ntest\n\nShe said, \"Sells she seashells on the seashore?\"\n";
}
Output:
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 C++ standards.
| 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) |
See also
| C documentation for Escape sequence |
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