String literal

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

C++ language

General topics
Preprocessor Comments	Keywords Escape sequences
Flow control
Conditional execution statements
if	switch
Iteration statements (loops)
for range-for (C++11)	while do-while
Jump statements
continue - break	goto - return
Functions
Function declaration
Lambda function expression
inline specifier
Dynamic exception specifications (until C++17*)
noexcept specifier (C++11)
Exceptions
throw-expression try block	handler
Namespaces
Namespace declaration	Namespace aliases
Types
Fundamental types Enumeration types Function types	Class/struct types Union types
Specifiers
const/volatile decltype (C++11) auto (C++11)	constexpr (C++11) consteval (C++20) constinit (C++20)
Storage duration specifiers
Initialization
Default-initialization Value-initialization Zero-initialization Copy-initialization Direct-initialization	Aggregate initialization List-initialization (C++11)   Constant initialization Reference initialization

Expressions
Value categories Order of evaluation	Operators Operator precedence
Alternative representations
Literals
Boolean - Integer - Floating-point
Character - String - nullptr (C++11)
User-defined (C++11)
Utilities
Attributes (C++11)
Types
typedef declaration
Type alias declaration (C++11)
Casts
Implicit conversions static_cast const_cast	Explicit conversions dynamic_cast reinterpret_cast
Memory allocation
new expression	delete expression
Classes
Class declaration Constructors this pointer	Access specifiers friend specifier
Class-specific function properties
Virtual function override specifier (C++11)   final specifier (C++11)	explicit (C++11) static
Special member functions
Default constructor Copy constructor Move constructor (C++11)	Copy assignment Move assignment (C++11) Destructor
Templates
Class template Function template	Template specialization Parameter packs (C++11)
Miscellaneous
Inline assembly	History of C++

 

Expressions

General
Value categories Order of evaluation Constant expressions Primary expressions	Lambda expressions (C++11) Requires expressions (C++20) Pack indexing expression (C++26) Potentially-evaluated expressions
Literals
Integer literals Floating-point literals Boolean literals Character literals	Escape sequences String literals Null pointer literal (C++11) User-defined literal (C++11)
Operators
Assignment operators Increment and decrement Arithmetic operators Logical operators Comparison operators Member access operators Other operators new-expression delete-expression throw-expression	alignof sizeof sizeof... (C++11) typeid noexcept (C++11) Fold expressions (C++17) Alternative representations of operators Precedence and associativity Operator overloading Default comparisons (C++20)
Conversions
Implicit conversions Explicit conversions Usual arithmetic conversions     User-defined conversion	const_cast static_cast dynamic_cast reinterpret_cast

 

Syntax

"s-char-seq (optional)"	(1)
R"d-char-seq (optional)(r-char-seq (optional))d-char-seq (optional)"	(2)	(since C++11)
L"s-char-seq (optional)"	(3)
LR"d-char-seq (optional)(r-char-seq (optional))d-char-seq (optional)"	(4)	(since C++11)
u8"s-char-seq (optional)"	(5)	(since C++11)
u8R"d-char-seq (optional)(r-char-seq (optional))d-char-seq (optional)"	(6)	(since C++11)
u"s-char-seq (optional)"	(7)	(since C++11)
uR"d-char-seq (optional)(r-char-seq (optional))d-char-seq (optional)"	(8)	(since C++11)
U"s-char-seq (optional)"	(9)	(since C++11)
UR"d-char-seq (optional)(r-char-seq (optional))d-char-seq (optional)"	(10)	(since C++11)

Explanation

s-char-seq	-	A sequence of one or more s-char s
s-char	-	One of a basic-s-char an escape sequence, as defined in escape sequences a universal character name, as defined in escape sequences
basic-s-char	-	A character from the translation character set, except the double-quote ", backslash \, or new-line character
d-char-seq	-	A sequence of one or more d-char s, at most 16 characters long
d-char	-	A character from the basic character set, except parentheses, backslash and spaces
r-char-seq	-	A sequence of one or more r-char s, except that it must not contain the closing sequence )d-char-seq"
r-char	-	A character from the translation character set

Syntax	Kind	Type	Encoding
(1,2)	ordinary string literal	const char[N]	ordinary literal encoding
(3,4)	wide string literal	const wchar_t[N]	wide literal encoding
(5,6)	UTF-8 string literal	const char[N] (until C++20) const char8_t[N] (since C++20)	UTF-8
(7,8)	UTF-16 string literal	const char16_t[N]	UTF-16
(9,10)	UTF-32 string literal	const char32_t[N]	UTF-32

In the types listed in the table above, N is the number of encoded code units, which is determined below.

Ordinary and UTF-8(since C++11) string literals are collectively referred to as narrow string literals.

Evaluating a string literal results in a string literal object with static storage duration. Whether all string literals are stored in nonoverlapping objects and whether successive evaluations of a string literal yield the same or a different object is unspecified.

The effect of attempting to modify a string literal object is undefined.

bool b = "bar" == 3 + "foobar"; // can be true or false, unspecified
 
const char* pc = "Hello";
char* p = const_cast<char*>(pc);
p[0] = 'M'; // undefined behavior

Raw string literals Raw string literals are string literals with a prefix containing R (syntaxes (2,4,6,8,10)). They do not escape any character, which means anything between the delimiters d-char-seq ( and )d-char-seq becomes part of the string. The terminating d-char-seq is the same sequence of characters as the initial d-char-seq. // OK: contains one backslash, // equivalent to "\\" R"(\)";   // OK: contains four \n pairs, // equivalent to "\\n\\n\\n\\n" R"(\n\n\n\n)";   // OK: contains one close-parenthesis, two double-quotes and one open-parenthesis, // equivalent to ")\"\"(" R"-()""()-";   // OK: equivalent to "\n)\\\na\"\"\n" R"a( )\ a"" )a";   // OK: equivalent to "x = \"\"\\y\"\"" R"(x = ""\y"")";   // R"<<(-_-)>>"; // Error: begin and end delimiters do not match // R"-()-"-()-"; // Error: )-" appears in the middle and terminates the literal

(since C++11)

Initialization

String literal objects are initialized with the sequence of code unit values corresponding to the string literal’s sequence of s-char s and r-char s(since C++11), plus a terminating null character (U+0000), in order as follows:

1) For each contiguous sequence of basic-s-char s, r-char s,(since C++11) simple escape sequences and universal character names, the sequence of character it denotes is encoded to a code unit sequence using the string literal’s associated character encoding. If a character lacks representation in the associated character encoding, then the program is ill-formed.

If the associated character encoding is stateful, the first such sequence is encoded beginning with the initial encoding state and each subsequent sequence is encoded beginning with the final encoding state of the prior sequence.

2) For each numeric escape sequence, given v as the integer value represented by the octal or hexadecimal number comprising the sequence of digits in the escape sequence, and T as the string literal’s array element type (see the table above):

• If v does not exceed the range of representable values of T, then the escape sequence contributes a single code unit with value v.
• Otherwise, if the string literal is of syntax (1) or (3), and(since C++11) v does not exceed the range of representable values of the corresponding unsigned type for the underlying type of T, then the escape sequence contributes a single code unit with a unique value of type T, that is congruent to v mod 2S, where S is the width of T.
• Otherwise, the program is ill-formed.

If the associated character encoding is stateful, all such sequences have no effect on encoding state.

3) Each conditional escape sequence contributes an implementation-defined code unit sequence.

If the associated character encoding is stateful, it is implementation-defined what effect these sequences have on encoding state.

Concatenation

Adjacent string literals are concatenated at translation phase 6 (after preprocessing):

• If the two string literals are of the same kind, the concatenated string literal is also of that kind.

If an ordinary string literal is adjacent to a wide string literal, the behavior is undefined.	(until C++11)
If an ordinary string literal is adjacent to a non-ordinary string literal, the concatenated string literal is of the kind of the latter. If a UTF-8 string literal is adjacent to a wide string literal, the program is ill-formed. Any other combination is conditionally supported with implementation-defined semantics. (until C++23) Any other combination is ill-formed. (since C++23)	(since C++11)

"Hello, " " world!" // at phase 6, the 2 string literals form "Hello, world!"
 
L"Δx = %" PRId16    // at phase 4, PRId16 expands to "d"
                    // at phase 6, L"Δx = %" and "d" form L"Δx = %d"

Unevaluated strings

The following contexts expect a string literal, but do not evaluate it:

• language linkage specification

static_assert literal operator name	(since C++11)
[[deprecated]]	(since C++14)
[[nodiscard]]	(since C++20)
deleted function body	(since C++26)

It is unspecified whether non-ordinary string literals are allowed in these contexts, except that a literal operator name must use an ordinary string literal(since C++11).	(until C++26)
Only ordinary string literals are allowed in these contexts. Each universal character name and each simple escape sequence in an unevaluated string is replaced by the member of the translation character set it denotes. An unevaluated string that contains a numeric escape sequence or a conditional escape sequence is ill-formed.	(since C++26)

Notes

String literals can be used to initialize character arrays. If an array is initialized like char str[] = "foo";, str will contain a copy of the string "foo".

String literals are convertible and assignable to non-const char* or wchar_t* in order to be compatible with C, where string literals are of types char[N] and wchar_t[N]. Such implicit conversion is deprecated.	(until C++11)
String literals are not convertible or assignable to non-const CharT*. An explicit cast (e.g. const_cast) must be used if such conversion is wanted.	(since C++11)

A string literal is not necessarily a null-terminated character sequence: if a string literal has embedded null characters, it represents an array which contains more than one string.

const char* p = "abc\0def"; // std::strlen(p) == 3, but the array has size 8

If a valid hexadecimal digit follows a hexadecimal escape sequence in a string literal, it would fail to compile as an invalid escape sequence. String concatenation can be used as a workaround:

//const char* p = "\xfff"; // error: hexadecimal escape sequence out of range
const char* p = "\xff""f"; // OK: the literal is const char[3] holding {'\xff','f','\0'}

Feature-test macro	Value	Std	Feature
__cpp_char8_t	202207L	(C++20) (DR20)	char8_t compatibility and portability fix (allow initialization of (unsigned) char arrays from UTF-8 string literals)
__cpp_raw_strings	200710L	(C++11)	Raw string literals
__cpp_unicode_literals	200710L	(C++11)	Unicode string literals

Example

Run this code

#include <iostream>
 
// array1 and array2 contains the same values:
char array1[] = "Foo" "bar";
char array2[] = {'F', 'o', 'o', 'b', 'a', 'r', '\0'};
 
const char* s1 = R"foo(
Hello
  World
)foo";
// same as
const char* s2 = "\nHello\n  World\n";
// same as
const char* s3 = "\n"
                 "Hello\n"
                 "  World\n";
 
const wchar_t* s4 = L"ABC" L"DEF"; // OK, same as
const wchar_t* s5 = L"ABCDEF";
const char32_t* s6 = U"GHI" "JKL"; // OK, same as
const char32_t* s7 = U"GHIJKL";
const char16_t* s9 = "MN" u"OP" "QR"; // OK, same as
const char16_t* sA = u"MNOPQR";
 
// const auto* sB = u"Mixed" U"Types";
        // before C++23 may or may not be supported by
        // the implementation; ill-formed since C++23
 
const wchar_t* sC = LR"--(STUV)--"; // OK, raw string literal
 
int main()
{
    std::cout << array1 << ' ' << array2 << '\n'
              << s1 << s2 << s3 << std::endl;
    std::wcout << s4 << ' ' << s5 << ' ' << sC
               << std::endl;
}

Output:

Foobar Foobar
 
Hello
  World
 
Hello
  World
 
Hello
  World
 
ABCDEF ABCDEF STUV

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 411 (P2029R4)	C++98	escape sequences in string literals were not allowed to map to multiple code units	allowed
CWG 1656 (P2029R4)	C++98	the characters denoted by numeric escape sequences in string literals were unclear	made clear
CWG 1759	C++11	a UTF-8 string literal might have code units that are not representable in char	char can represent all UTF-8 code units
CWG 1823	C++98	whether string literals are distinct was implementation-defined	distinctness is unspecified, and same string literal can yield different object
CWG 2333 (P2029R4)	C++11	it was unclear whether numeric escape sequences were allowed in UTF-8/16/32 string literals	made clear
CWG 2870	C++11	the concatenation result of two ordinary string literals was unclear	made clear
P1854R4	C++98	ordinary and wide string literals with non-encodable characters were conditionally-supported	programs with such literals are ill-formed
P2029R4	C++98	1. it was unclear whether string literals     could contain non-encodable characters 2. it was unclear whether string literals could     contain numeric escape sequences such     that the code units they represent are not     representable in the literals' array element type	1. made conditionally-supported for     ordinary and wide string literals 2. ill-formed if the code units are     neither representable in the     unsigned integer type corresponding     to the underlying type

References

• C++23 standard (ISO/IEC 14882:2024):

• 5.13.5 String literals [lex.string]

• C++20 standard (ISO/IEC 14882:2020):

• 5.13.5 String literals [lex.string]

• C++17 standard (ISO/IEC 14882:2017):

• 5.13.5 String literals [lex.string]

• C++14 standard (ISO/IEC 14882:2014):

• 2.14.5 String literals [lex.string]

• C++11 standard (ISO/IEC 14882:2011):

• 2.14.5 String literals [lex.string]

• C++03 standard (ISO/IEC 14882:2003):

• 2.13.4 String literals [lex.string]

• C++98 standard (ISO/IEC 14882:1998):

• 2.13.4 String literals [lex.string]

See also

user-defined literals(C++11)	literals with user-defined suffix
C documentation for String literals