Manual browser: limits(3)

LIMITS(3)

Library Functions Manual

LIMITS(3)

NAME

limits — standard limits

SYNOPSIS

#include <limits.h>

DESCRIPTION

The <limits.h> header defines various compile-time and runtime limits. These can be grouped into three categories:

Compile-time limits defined in a header file.
Runtime system limits that are not associated with a file or directory; see sysconf(3).
Runtime limits that are associated with a file or directory; see pathconf(2).

The <limits.h> header has been standardized by at least three entities.

ISO Limits

The limits defined by the ISO/IEC 9899:1999 (“ISO C99”) standard are all compile-time limits. The numerical (integer) limits are:

Constant	Type	Minimum value
CHAR_BIT	char	8
SCHAR_MAX	signed char	127
SCHAR_MIN	signed char	-127
UCHAR_MAX	unsigned char	255
INT_MAX	int	32767
INT_MIN	int	-32767
UINT_MAX	unsigned int	65535
SHRT_MIN	short	-32767
SHRT_MAX	short	32767
USHRT_MAX	unsigned short	65535
LONG_MAX	long int	2147483647
LONG_MIN	long int	-2147483647
ULONG_MAX	unsigned long int	4294967295
LLONG_MAX	long long int	9223372036854775807
LLONG_MIN	long long int	-9223372036854775807
ULLONG_MAX	unsigned long long int	18446744073709551615
MB_LEN_MAX	-	1

All listed limits may vary across machines and operating systems. The standard guarantees only that the implementation-defined values are equal or greater in absolute value to those shown. The values permit a system with 16-bit integers using one's complement arithmetic.

Depending whether the system defines char as signed or unsigned, the maximum and minimum values are:

Constant	Type	Minimum value
CHAR_MAX	char	either SCHAR_MAX or UCHAR_MAX
CHAR_MIN	char	either SCHAR_MIN or 0

The two special cases, CHAR_BIT and MB_LEN_MAX, define the number of bits in char and the maximum number of bytes in a multibyte character constant, respectively.

POSIX Limits

The POSIX.1 standard specifies numerous limits related to the operating system. For each limit, a separate constant prefixed with “_POSIX_” defines the lowest value that the limit is allowed to have on any POSIX compliant system. For instance, _POSIX_OPEN_MAX defines the minimum upper bound permitted by POSIX for the number of files that a single process may have open at any time. This ensures that a portable program can safely reach these limits without prior knowledge about the actual limits used in a particular system.

As the limits are not necessary invariant, pathconf(2) and sysconf(3) should be used to determine the actual value of a limit at runtime. The manual pages of these two functions also contain a more detailed description of the limits available in NetBSD.

XSI Limits

Also the X/Open System Interface Extension (XSI) specifies few limits. In NetBSD these are limited to LONG_BIT (the number of bits in long), WORD_BIT (the number of bits in a “word”), and few limits related to float and double.