Integer constant - cppreference.com (original) (raw)

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

Contents

[edit] Syntax

An integer constant is a non-lvalue expression of the form
decimal-constant integer-suffix (optional) (1)
octal-constant integer-suffix (optional) (2)
hex-constant integer-suffix (optional) (3)
binary-constant integer-suffix (optional) (4) (since C23)

where

Optional single quotes (') may be inserted between the digits as a separator. They are ignored by the compiler. (since C23)

[edit] Explanation

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

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

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

  4. Binary integer constant (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; // C23

The following variables are also initialized to the same value:

unsigned long long l1 = 18446744073709550592ull; // C99 unsigned long long l2 = 18'446'744'073'709'550'592llu; // C23 unsigned long long l3 = 1844'6744'0737'0955'0592uLL; // C23 unsigned long long l4 = 184467'440737'0'95505'92LLU; // C23

[edit] The type of the integer constant

The type of the integer constant 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 constants

suffix decimal bases other bases
no suffix int long int unsigned long int (until C99) long long int (since C99) int unsigned int long int unsigned long int long long int(since C99) unsigned long long int(since C99)
u or U unsigned int unsigned long int unsigned long long int(since C99) unsigned int unsigned long int unsigned long long int(since C99)
l or L long int unsigned long int(until C99) long long int(since C99) long int unsigned long int long long int(since C99) unsigned long long int(since C99)
both l/L and u/U unsigned long int unsigned long long int(since C99) unsigned long int unsigned long long int(since C99)
ll or LL long long int(since C99) long long int(since C99) unsigned long long int(since C99)
both ll/LL and u/U unsigned long long int(since C99) unsigned long long int(since C99)
wb or WB _BitInt(N) where the width N is the smallest N greater than 1 which can accommodate the value and the sign bit(since C23) _BitInt(N) where the width N is the smallest N greater than 1 which can accommodate the value and the sign bit(since C23)
both wb/WB and u/U unsigned _BitInt(N) where the width N is the smallest N greater than 0 which can accommodate the value(since C23) unsigned _BitInt(N) where the width N is the smallest N greater than 0 which can accommodate the value(since C23)

If the value of the integer constant is too big to fit in any of the types allowed by suffix/base combination, it does not have suffixes wb, WB, uwb, or UWB(since C23) and the compiler supports extended integer types (such as __int128), the constant may be given the extended integer type; otherwise, the program is ill-formed.

[edit] Notes

Letters in the integer constants are case-insensitive: 0xDeAdBaBeU and 0XdeadBABEu represent the same number (one exception is the long-long-suffix, which is either ll or LL, never lL or Ll)(since C99).

There are no negative integer constants. Expressions such as -1 apply the unary minus operator to the value represented by the constant.

When used in a controlling expression of #if or #elif, all signed integer constants act as if they have type intmax_t and all unsigned integer constants act as if they have type uintmax_t. (since C99)

Integer constants may be used in integer constant expressions.

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

int x = 0xE+2; // error int y = 0xa+2; // OK int z = 0xE +2; // OK int q = (0xE)+2; // OK

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

[edit] Example

#include <inttypes.h> #include <stdio.h>   int main(void) { printf("123 = %d\n", 123); printf("0123 = %d\n", 0123); printf("0x123 = %d\n", 0x123); printf("12345678901234567890ull = %llu\n", 12345678901234567890ull); // the type is a 64-bit type (unsigned long long or possibly unsigned long) // even without a long suffix printf("12345678901234567890u = %"PRIu64"\n", 12345678901234567890u );   // printf("%lld\n", -9223372036854775808); // Error: // the value 9223372036854775808 cannot fit in signed long long, which // is the biggest type allowed for unsuffixed decimal integer constant   printf("%llu\n", -9223372036854775808ull ); // unary minus applied to unsigned value subtracts it from 2^64, // this gives unsigned 9223372036854775808   printf("%lld\n", -9223372036854775807ll - 1); // correct way to form signed value -9223372036854775808 }

Output:

123 = 123 0123 = 83 0x123 = 291 12345678901234567890ull = 12345678901234567890 12345678901234567890u = 12345678901234567890 9223372036854775808 -9223372036854775808

[edit] References

[edit] See also