Numeric String¶

A numeric string, is a string that contains a numeric value, or can be easily converted from string to numeric (integer or float).

Some of such strings are obvious, and commonly used: 123 or '45.67'. HereDocs string may also be a numeric string.

Non numeric strings are mostly obvious too, such as: abc or '中文'.

Then, there are some various cases:

‘123db’: leading strings, starting with digits and finished by non-digit characters are converted as much as possible.
‘2e3’: the exponent is recognized: when e (case insensitive), is between two digit, the float notation is used. This is 2000.
‘+00’, ‘-10’: leading + and - are handled. There can only be one, unlike for hardcoded integers.
‘ 20 ‘: leading and trailing spaces, tabulations, new lines, new feed are omitted.
str_repeat(‘0’, 10001).2: PHP tries to convert as much as possible. Leading 0 will basically be ignored, however numerous they are.
(int) str_repeat(‘1’, 10001): PHP returns 0 when conversion fails
str_repeat(‘1’, 10001) + 0: PHP returns INF when the conversion fails and is silent.
‘三’, ‘CM’: other ways of counting are not recognized

A string may be checked with the is_numeric() function. It cannot be checked with is_int() and is_float().