Escape sequences

< c‎ | language

Escape sequences are used to represent certain special characters within string literals and character constants.

The following escape sequences are available. ISO C requires a diagnostic if the backslash is followed by any character not listed here:

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
Universal character names
\unnnn (since C99) Unicode value in allowed range;
may result in several code units		 code point U+nnnn
\Unnnnnnnn (since C99) Unicode value in allowed range;
may result in several code units		 code point U+nnnnnnnn

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, or a surrogate code point (the range 0xD800-0xDFFF, inclusive), 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.

A universal character name corresponding to a code pointer greater than 0x10FFFF (which is undefined in ISO/ISC 10646) can be used in character constants and string literals. Such usage is not allowed in C++20.

 (since C99)

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 byte or byte sequence.

Octal escape sequences have a length 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 or character constant (char, char16_t, char32_t (since C11), or wchar_t), the result is unspecified.

A universal character name in a narrow string literal or a 16-bit string literal (since C11) 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) (since C11).

 (since C99)

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 "??/"

Example

#include <stdio.h>
 
int main(void)
{
    printf("This\nis\na\ntest\n\nShe said, \"How are you?\"\n");
}

Output:

This
is
a
test
 
She said, "How are you?"

References

  • C17 standard (ISO/IEC 9899:2018):
  • 5.2.2 Character display semantics (p: 18-19)
  • 6.4.3 Universal Character names (p: 44)
  • 6.4.4.4 Character constants (p: 48-50)
  • C11 standard (ISO/IEC 9899:2011):
  • 5.2.2 Character display semantics (p: 24-25)
  • 6.4.3 Universal Character names (p: 61)
  • 6.4.4.4 Character constants (p: 67-70)
  • C99 standard (ISO/IEC 9899:1999):
  • 5.2.2 Character display semantics (p: 19-20)
  • 6.4.3 Universal Character names (p: 53)
  • 6.4.4.4 Character constants (p: 59-61)
  • C89/C90 standard (ISO/IEC 9899:1990):
  • 2.2.2 Character display semantics
  • 3.1.3.4 Character constants

See also