C Programming/limits.h

limits.h includes definitions of the characteristics of common variable types. The values are implementation specific, but may not be of lower magnitude than certain specified values in a conforming C implementation.

The C99 standard also specifies the  header file, which provides names and limits for explicitly-sized platform-independent integer datatypes (e.g.   for a 32-bit signed integer).

Member constants
The "minimum-magnitude value" column is the minimum possible magnitude for this constant as specified by the standard. In particular,  values represent the minimum magnitude representable in the rarely-used one's complement and sign-magnitude forms. Most implementations will have larger magnitudes for at least some of these numbers. For instance:
 * Two's complement implementations have  equal to −128 (and similarly for all other   values).
 * 32-bit implementations will set  equal to +2,147,483,647 (and likewise for   and  )
 * Unicode-supporting implementations will set  to 4 or more.
 * Many DSPs have  equal to 16 or more.