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integer literal

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

Syntax

An integer literal is a primary expression of the form.

decimal-literal integer-suffix(optional)	(1)
octal-literal integer-suffix(optional)	(2)
hex-literal integer-suffix(optional)	(3)
binary-literal integer-suffix(optional)	(4)	(since C++14)

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 sequence 0x or the character sequence 0X 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 sequence 0b or the character sequence 0B 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 character u or the character U)
long-suffix (the character l or the character L) or the long-long-suffix (the character sequence ll or the character sequence LL) (since C++11)

Optional single quotes(') may be inserted between the digits as a separator. They are ignored by the compiler. (since C++14)

Explanation

1) Decimal integer literal (base 10, the first digit is the most significant)

2) Octal integer literal (base 8, the first digit is the most significant)

3) Hexadecimal integer literal (base 16, the first digit is the most significant, the letters 'a' through 'f' represent values (decimal) 10 through 15)

4) Binary integer literal (base 2, the first digit is the most significant)

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

The following variables are also initialized to the same value:

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

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 which integer-suffix was used.

Types allowed for integer literals
suffix	decimal bases	binary, octal, or hexadecimal bases
no suffix	`int` `long int` `long long int`(since C++11).	`int` `unsigned int` `long int` `unsigned long int` `long long int`(since C++11) `unsigned long long int`(since C++11).
`u` or `U`	`unsigned int` `unsigned long int` `unsigned long long int`(since C++11).	`unsigned int` `unsigned long int` `unsigned long long int`(since C++11).
`l` or `L`	`long int` `unsigned long int`(until C++11) `long long int`(since C++11).	`long int` `unsigned long int` `long long int`(since C++11) `unsigned long long int`(since C++11).
both `l`/`L` and `u`/`U`	`unsigned long int` `unsigned long long int`(since C++11).	`unsigned long int`(since C++11) `unsigned long long int`(since C++11).
`ll` or `LL`	`long long int`(since C++11)	`long long int`(since C++11) `unsigned long long int`(since C++11).
both `ll`/`LL` and `u`/`U`	`unsigned long long int`(since C++11)	`unsigned long long int`(since C++11)

If the value of the integer literal is too big to fit in any of the types allowed by suffix/base combination and the compiler supports extended integer types (such as __int128) the literal may be given the extended integer type -- otherwise the program is ill-formed.

Notes

Letters in the integer literals are case-insensitive: 0xDeAdBeEfU and 0XdeadBEEFu represent the same number (one exception is the long-long-suffix, which is either ll or LL, never lL or Ll).

There are no negative integer literals. Expressions such as -1 apply the unary 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 in long int are allowed to have the type unsigned long int.

When used in a controlling expression of #if or #elif, all signed integer constants act as if they have type std::intmax_t and all unsigned integer constants act as if they have type std::uintmax_t.

Due to maximal munch, hexadecimal integer literals ending in e and E, when followed by the operators + or -, must be separated from the operator with whitespace or parentheses in the source:

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

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

Example

#include <iostream>
 
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 literal
     std::cout << -9223372036854775808u << '\n'; // unary minus applied to unsigned
                // value subtracts it from 2^64, this gives 9223372036854775808
     std::cout << -9223372036854775807 - 1 << '\n'; // correct way to calculate
                                                    // the value -9223372036854775808
}

Output: