Allows values of integer type to be used in expressions directly.
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An integer constant is anon-lvalue expression of the form
| decimal-constantinteger-suffix (optional) | (1) | ||||||||
| octal-constantinteger-suffix (optional) | (2) | ||||||||
| hex-constantinteger-suffix (optional) | (3) | ||||||||
| binary-constantinteger-suffix (optional) | (4) | (since C23) | |||||||
where
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)0) followed by zero or more octal digits (0,1,2,3,4,5,6,7)0x 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)0b or the character sequence0B followed by one or more binary digits (0,1)u or the characterU)l or the characterL)or thelong-long-suffix (the character sequencell or the character sequenceLL)(since C99)wb or the character sequenceWB)(since C23)Optional single quotes ( | (since C23) |
a throughf represent the decimal values 10 through 15).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:
unsignedlonglong l1= 18446744073709550592ull;// C99unsignedlonglong l2=18'446'744'073'709'550'592llu;// C23unsignedlonglong l3=1844'6744'0737'0955'0592uLL;// C23unsignedlonglong l4=184467'440737'0'95505'92LLU;// C23
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 whichinteger-suffix was used.
| suffix | decimal bases | other bases |
|---|---|---|
| no suffix | int longint | int unsignedint |
u orU | unsignedint unsignedlongint | unsignedint unsignedlongint |
l orL | longint unsignedlongint(until C99) | longint unsignedlongint |
bothl/L andu/U | unsignedlongint unsignedlonglongint(since C99) | unsignedlongint unsignedlonglongint(since C99) |
ll orLL | longlongint(since C99) | longlongint(since C99) unsignedlonglongint(since C99) |
bothll/LL andu/U | unsignedlonglongint(since C99) | unsignedlonglongint(since C99) |
wb orWB | _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) |
bothwb/WB andu/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 suffixeswb,WB,uwb, orUWB(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.
Letters in the integer constants are case-insensitive:0xDeAdBaBeU and0XdeadBABEu represent the same number (one exception is thelong-long-suffix, which is eitherll orLL, neverlL orLl)(since C99).
There are no negative integer constants. Expressions such as-1 apply theunary 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 typeintmax_t and all unsigned integer constants act as if they have typeuintmax_t. | (since C99) |
Integer constants may be used ininteger constant expressions.
Due tomaximal munch, hexadecimal integer constants ending ine andE, when followed by the operators+ or-, must be separated from the operator with whitespace or parentheses in the source:
int x=0xE+2;// errorint y=0xa+2;// OKint z=0xE+2;// OKint q=(0xE)+2;// OK
Otherwise, a single invalid preprocessing number token is formed, which causes further analysis to fail.
#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 suffixprintf("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 = 1230123 = 830x123 = 29112345678901234567890ull = 1234567890123456789012345678901234567890u = 123456789012345678909223372036854775808-9223372036854775808
C++ documentation forInteger literal |
