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humanize_number – format a number into a human readable form



System Utilities Library (libutil, -lutil)


#include <libutil.h>

humanize_number(char *buf, size_t len, int64_t number, const char *suffix, int scale, int flags);


The humanize_number() function formats the signed 64-bit quantity given in number into buf. A space and then suffix is appended to the end. The buffer pointed to by buf must be at least len bytes long.

If the formatted number (including suffix) would be too long to fit into buf, then divide number by 1024 until it will. In this case, prefix suffix with the appropriate designator. The humanize_number() function follows the traditional computer science conventions by default, rather than the IEE/IEC (and now also SI) power of two convention or the power of ten notion. This behaviour however can be altered by specifying the HN_DIVISOR_1000 and HN_IEC_PREFIXES flags.

The traditional (default) prefixes are:
Prefix Description Multiplier Multiplier 1000x
(note) kilo 1024 1000
M mega 1048576 1000000
G giga 1073741824 1000000000
T tera 1099511627776 1000000000000
P peta 1125899906842624 1000000000000000
E exa 1152921504606846976 1000000000000000000

Note: An uppercase K indicates a power of two, a lowercase k a power of ten.

The IEE/IEC (and now also SI) power of two prefixes are:
Prefix Description Multiplier
Ki kibi 1024
Mi mebi 1048576
Gi gibi 1073741824
Ti tebi 1099511627776
Pi pebi 1125899906842624
Ei exbi 1152921504606846976

The len argument must be at least 4 plus the length of suffix, in order to ensure a useful result is generated into buf. To use a specific prefix, specify this as scale (multiplier = 1024 ^ scale; when HN_DIVISOR_1000 is specified, multiplier = 1000 ^ scale ). This cannot be combined with any of the scale flags below.

The following flags may be passed in scale:
HN_AUTOSCALE Format the buffer using the lowest multiplier possible.
HN_GETSCALE Return the prefix index number (the number of times number must be divided to fit) instead of formatting it to the buffer.

The following flags may be passed in flags:
HN_DECIMAL If the final result is less than 10, display it using one decimal place.
HN_NOSPACE Do not put a space between number and the prefix.
HN_B Use ‘B’ (bytes) as prefix if the original result does not have a prefix.
  Divide number with 1000 instead of 1024.
  Use the IEE/IEC notion of prefixes (Ki, Mi, Gi...). This flag has no effect when HN_DIVISOR_1000 is also specified.


Upon success, the humanize_number function returns the number of characters that would have been stored in buf (excluding the terminating NUL) if buf was large enough, or -1 upon failure. Even upon failure, the contents of buf may be modified. If HN_GETSCALE is specified, the prefix index number will be returned instead.




The HN_DIVISOR_1000 and HN_IEC_PREFIXES flags conform to ISO/IEC Std 80000-13:2008 and IEEE Std 1541-2002.


The humanize_number() function first appeared in NetBSD and then in FreeBSD 5.3 . The HN_IEC_PREFIXES flag was introduced in FreeBSD 9.0 .


For numbers greater than 999 using buffer length of 4 and less can cause rounding errors. When using HN_IEC_PREFIXES the same error occurs for buffer length of 5 or less.

HUMANIZE_NUMBER (3) October 7, 2013

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