Integer types and constants

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Example

Signed integers can be of these types (the int after short, or long is optional):

signed char c = 127; /* required to be 1 byte, see remarks for further information. */
signed short int si = 32767; /* required to be at least 16 bits. */
signed int i = 32767; /* required to be at least 16 bits */
signed long int li = 2147483647; /* required to be at least 32 bits. */
C99
signed long long int li = 2147483647; /* required to be at least 64 bits */

Each of these signed integer types has an unsigned version.

unsigned int i = 65535;
unsigned short = 2767;
unsigned char = 255;

For all types but char the signed version is assumed if the signed or unsigned part is omitted. The type char constitutes a third character type, different from signed char and unsigned char and the signedness (or not) depends on the platform.

Different types of integer constants (called literals in C jargon) can be written in different bases, and different width, based on their prefix or suffix.

/* the following variables are initialized to the same value: */
int d = 42;   /* decimal constant (base10) */
int o = 052;  /* octal constant (base8) */
int x = 0xaf; /* hexadecimal constants (base16) */
int X = 0XAf; /* (letters 'a' through 'f' (case insensitive) represent 10 through 15) */

Decimal constants are always signed. Hexadecimal constants start with 0x or 0X and octal constants start just with a 0. The latter two are signed or unsigned depending on whether the value fits into the signed type or not.

/* suffixes to describe width and signedness : */
long int i = 0x32; /* no suffix represent int, or long int */
unsigned int ui = 65535u; /* u or U represent unsigned int, or long int */
long int li = 65536l; /* l or L represent long int */

Without a suffix the constant has the first type that fits its value, that is a decimal constant that is larger than INT_MAX is of type long if possible, or long long otherwise.

The header file <limits.h> describes the limits of integers as follows. Their implementation-defined values shall be equal or greater in magnitude (absolute value) to those shown below, with the same sign.

MacroTypeValue
CHAR_BITsmallest object that is not a bit-field (byte)8
SCHAR_MINsigned char-127 / -(27 - 1)
SCHAR_MAXsigned char+127 / 27 - 1
UCHAR_MAXunsigned char255 / 28 - 1
CHAR_MINcharsee below
CHAR_MAXcharsee below
SHRT_MINshort int-32767 / -(215 - 1)
SHRT_MAXshort int+32767 / 215 - 1
USHRT_MAXunsigned short int65535 / 216 - 1
INT_MINint-32767 / -(215 - 1)
INT_MAXint+32767 / 215 - 1
UINT_MAXunsigned int65535 / 216 - 1
LONG_MINlong int-2147483647 / -(231 - 1)
LONG_MAXlong int+2147483647 / 231 - 1
ULONG_MAXunsigned long int4294967295 / 232 - 1
C99
MacroTypeValue
LLONG_MINlong long int-9223372036854775807 / -(263 - 1)
LLONG_MAXlong long int+9223372036854775807 / 263 - 1
ULLONG_MAXunsigned long long int18446744073709551615 / 264 - 1

If the value of an object of type char sign-extends when used in an expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the value of CHAR_MAX shall be the same as that of SCHAR_MAX . If the value of an object of type char does not sign-extend when used in an expression, the value of CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of UCHAR_MAX.

C99

The C99 standard added a new header, <stdint.h>, which contains definitions for fixed width integers. See the fixed width integer example for a more in-depth explanation.

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2016-09-14
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