Escape sequences

• 1 Range of universal character names
  • 1.1 Named universal character escapes
• 2 Notes
• 3 Example
• 4 Defect reports
• 5 See also

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.

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.

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.

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.

Named universal character escapes

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.

[edit] 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.

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)

[edit] 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?"

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also

• ASCII chart