$isnumber()

Synopsis

$isnumber(<text>)
$isnumber(b<base-num> <text>)
$isnumber(<text> b<base-num>)

Technical

Tests whether the number argument can be consumed as one integer segment, optionally followed by a literal decimal point and a second integer segment. At least one segment must contain a number, and the entire number argument must be consumed. The function tests syntax; it does not return the numeric value.

The default base is 0, which auto-detects decimal, leading-zero octal, and 0x hexadecimal syntax. With an explicit base, digits must be legal in that base. If a decimal point occurs with base 0, the segment after it is parsed in base 10; otherwise both segments use the chosen base.

A lowercase b introduces the base argument. It can be the first or second word. In first position it is recognized only when its suffix contains decimal digits, optionally preceded by -; otherwise that word is treated as the number. In second position any word starting with lowercase b is treated as a base argument, using base-detecting integer conversion of its suffix. Bases outside 0 through 36 revert to 0. Use 0 or 2 through 36: the implementation also passes 1 to the C library, where it is an unsupported base with no reliable result.

The first word and a second-position base are ordinary unquoted words. A number following a first-position base uses function-argument word parsing. Text beyond the number and optional base is ignored; this does not validate a whole multiword input string.

Each segment uses the C integer parser, which accepts a leading sign. Thus +3, -3, .5, 3., and even 3.-4 qualify. A bare . does not. Exponent notation, inf, and nan are not accepted. Overflow is not checked, so 1 does not establish that the value fits an integer or is a valid floating-point literal.

Practical

Use this to check number syntax in an indicated base, such as octal or hexadecimal. Its two-segment rules differ from a normal floating-point parser, so do not treat it as a general numeric conversion or range check.

Returns

1 if the number argument passes the syntax test, otherwise 0. Missing or empty number input returns the empty string.

Examples

Source

Registered and implemented as function_isnumber in source/functions.c. First-position base recognition (is_number) and base conversion (my_atol) are in source/ircaux.c.