Integer constant

 

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

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 哋它亢23)

where

• decimal-constant 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-constant is the digit zero (0) followed by zero or more octal digits (0, 1, 2, 3, 4, 5, 6, 7)
• hex-constant 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-constant 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 of the following (except the unsigned prefix can be combined with one of the others; if two suffixes are used they can 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 哋它亢99)
• bit-precise-int-suffix (the character sequence wb or the character sequence WB) (since 哋它亢23)

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

(since 哋它亢23)

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; // 哋它亢23

The following variables are also initialized to the same value:

unsigned long long l1 = 18446744073709550592ull; // 哋它亢99
unsigned long long l2 = 18'446'744'073'709'550'592llu; // 哋它亢23
unsigned long long l3 = 1844'6744'0737'0955'0592uLL; // 哋它亢23
unsigned long long l4 = 184467'440737'0'95505'92LLU; // 哋它亢23

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 哋它亢99) long long int (since 哋它亢99)	int unsigned int long int unsigned long int long long int(since 哋它亢99) unsigned long long int(since 哋它亢99)
u or U	unsigned int unsigned long int unsigned long long int(since 哋它亢99)	unsigned int unsigned long int unsigned long long int(since 哋它亢99)
l or L	long int unsigned long int(until 哋它亢99) long long int(since 哋它亢99)	long int unsigned long int long long int(since 哋它亢99) unsigned long long int(since 哋它亢99)
both l/L and u/U	unsigned long int unsigned long long int(since 哋它亢99)	unsigned long int unsigned long long int(since 哋它亢99)
ll or LL	long long int(since 哋它亢99)	long long int(since 哋它亢99) unsigned long long int(since 哋它亢99)
both ll/LL and u/U	unsigned long long int(since 哋它亢99)	unsigned long long int(since 哋它亢99)
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 哋它亢23)	_BitInt(N) where the width N is the smallest N greater than 1 which can accommodate the value and the sign bit(since 哋它亢23)
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 哋它亢23)	unsigned _BitInt(N) where the width N is the smallest N greater than 0 which can accommodate the value(since 哋它亢23)

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 哋它亢23) 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.

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 哋它亢99).

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 哋它亢99)

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.

Example

Run this code

#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

References

• 哋它亢23 standard (ISO/IEC 9899:2023):

• 6.4.4.1 Integer constants (p: 57-60)

• 哋它亢17 standard (ISO/IEC 9899:2018):

• 6.4.4.1 Integer constants (p: 45-46)

• 哋它亢11 standard (ISO/IEC 9899:2011):

• 6.4.4.1 Integer constants (p: 62-64)

• 哋它亢99 standard (ISO/IEC 9899:1999):

• 6.4.4.1 Integer constants (p: 54-56)

• 哋它亢89/C90 standard (ISO/IEC 9899:1990):

• 3.1.3.2 Integer constants