Allows values of integer type to be used in expressions directly.

[edit]Syntax

An integer literal has the form

where

• decimal-literal is a non-zero decimal digit (1,2,3,4,5,6,7,8,9), followed by zero or more decimal digits (0,1,2,3,4,5,6,7,8,9)
• octal-literal is the digit zero (0) followed by zero or more octal digits (0,1,2,3,4,5,6,7)
• hex-literal is the character sequence0x or the character sequence0X followed by one or more hexadecimal digits (0,1,2,3,4,5,6,7,8,9,a,A,b,B,c,C,d,D,e,E,f,F)
• binary-literal is the character sequence0b or the character sequence0B followed by one or more binary digits (0,1)
• integer-suffix, if provided, may contain one or both of the following (if both are provided, they may appear in any order:

• unsigned-suffix (the characteru or the characterU)
• one of

• long-suffix (the characterl or the characterL)

An integer literal (as any literal) is aprimary expression.

[edit]Explanation

The first digit of an integer literal is the most significant.

Example. The following variables are initialized to the same value:

int d=42;int o=052;int x=0x2a;int X=0X2A;int b=0b101010;// C++14

Example. The following variables are also initialized to the same value:

unsignedlonglong l1= 18446744073709550592ull;// C++11unsignedlonglong l2=18'446'744'073'709'550'592llu;// C++14unsignedlonglong l3=1844'6744'0737'0955'0592uLL;// C++14unsignedlonglong l4=184467'440737'0'95505'92LLU;// C++14

[edit]The type of the literal

The type of the integer literal is the first type in which the value can fit, from the list of types which depends on which numeric base and whichinteger-suffix was used:

If the value of the integer literalthat does not havesize-suffix(since C++23) is too big to fit in any of the types allowed by suffix/base combination and the compiler supports an extended integer type (such as__int128) which can represent the value of the literal, the literal may be given that extended integer type — otherwise the program is ill-formed.

[edit]Notes

Letters in the integer literals are case-insensitive:0xDeAdBeEfU and0XdeadBEEFu represent the same number(one exception is thelong-long-suffix, which is eitherll orLL, neverlL orLl)(since C++11).

There are no negative integer literals. Expressions such as-1 apply theunary minus operator to the value represented by the literal, which may involve implicit type conversions.

In C prior to C99 (but not in C++), unsuffixed decimal values that do not fit inlongint are allowed to have the typeunsignedlongint.

Due tomaximal munch, hexadecimal integer literals ending ine andE, when followed by the operators+ or-, must be separated from the operator with whitespace or parentheses in the source:

auto x=0xE+2.0;// errorauto y=0xa+2.0;// OKauto z=0xE+2.0;// OKauto q=(0xE)+2.0;// OK

Otherwise, a single invalid preprocessing number token is formed, which causes further analysis to fail.

[edit]Example

#include <cstddef>#include <iostream>#include <type_traits> int main(){std::cout<<123<<'\n'<<0123<<'\n'<<0x123<<'\n'<<0b10<<'\n'<< 12345678901234567890ull<<'\n'<< 12345678901234567890u<<'\n';// the type is unsigned long long// even without a long long suffix //  std::cout << -9223372036854775808 << '\n'; // error: the value// 9223372036854775808 cannot fit in signed long long, which is the// biggest type allowed for unsuffixed decimal integer literalstd::cout<<-9223372036854775808u<<'\n';// unary minus applied to unsigned// value subtracts it from 2^64, this gives 9223372036854775808std::cout<<-9223372036854775807-1<<'\n';// correct way to calculate// the value -9223372036854775808 #if __cpp_size_t_suffix >= 202011L // C++23    static_assert(std::is_same_v<decltype(0UZ),std::size_t>);    static_assert(std::is_same_v<decltype(0Z),std::make_signed_t<std::size_t>>);#endif}

12383291212345678901234567890123456789012345678909223372036854775808-9223372036854775808

[edit]Defect reports

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

[edit]References

[edit]See also

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