number_format() returns a
formatted version of
number. This function accepts either one, two or
four parameters (not three):
If only one parameter is given,
number will be formatted without decimals, but with
a comma (",") between every group of thousands.
If two parameters are given,
number will be formatted with
decimals decimals with a dot (".") in front, and
a comma (",") between every group of thousands.
If all four parameters are given,
number will be formatted with decimals decimals, dec_point instead of a dot (".")
before the decimals and
thousands_sep instead of a comma (",") between every
group of thousands.
注: Only the first character of thousands_sep is used. For example, if you use foo as thousands_sep on the number 1000, number_format() will return 1f000.