String literal

Syntax

Explanation

Each s-char (originally from non-raw string literals) or r-char (originally from raw string literals) (since C++11) initializes the corresponding element(s) in the string literal object. An s-char or r-char (since C++11) corresponds to more than one element if and only if it is represented by a sequence of more than one code units in the string literal's associated character encoding.

Each numeric escape sequence corresponds to a single element. If the value specified by the escape sequence fits within the unsigned version of the element type, the element has the specified value (possibly after conversion to the element type); otherwise (the specified value is out of range), the string literal is ill-formed. (since C++23).

Concatenation

String literals placed side-by-side are concatenated at translation phase 6 (after the preprocessor). That is, "Hello," " world!" yields the (single) string "Hello, world!". If the two strings have the same encoding prefix (or neither has one), the resulting string will have the same encoding prefix (or no prefix).

L"Δx = %" PRId16 // at phase 4, PRId16 expands to "d"
                 // at phase 6, L"Δx = %" and "d" form L"Δx = %d"

Notes

The null character ('\0', L'\0', char16_t(), etc) is always appended to the string literal: thus, a string literal "Hello" is a const char[6] holding the characters 'H', 'e', 'l', 'l', 'o', and '\0'.

The encoding of ordinary string literals (1) and wide string literals (2) is implementation-defined. For example, gcc selects them with the command line options -fexec-charset and -fwide-exec-charset.

String literals have static storage duration, and thus exist in memory for the life of the program.

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".

Whether string literals can overlap and whether successive evaluations of a string-literal yield the same object is unspecified. That means that identical string literals may or may not compare equal when compared by pointer.

bool b = "bar" == 3+"foobar"; // could be true or false, implementation-defined

Attempting to modify a string literal results in undefined behavior: they may be stored in read-only storage (such as .rodata) or combined with other string literals:

const char* pc = "Hello";
char* p = const_cast<char*>(pc);
p[0] = 'M'; // undefined behavior

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

Although mixed wide string literal concatenation is allowed in C++11, all known C++ compilers reject such concatenation, and its usage experience is unknown. As a result, allowance of mixed wide string literal concatenation is removed in C++23.

Example

#include <iostream>
 
char array1[] = "Foo" "bar";
// same as
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;
}

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.

References

• C++23 standard (ISO/IEC 14882:2023):
• 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