General Numeric - The GNU C Library

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##### 7.6.1.1 Generic Numeric Formatting Parameters

These are the standard members of `struct lconv`; there may be others.

`char *decimal_point`
`char *mon_decimal_point`
  These are the decimal-point separators used in formatting non-monetary and monetary quantities, respectively. In the ‘`C`’ locale, the value of `decimal_point` is `"."`, and the value of `mon_decimal_point` is `""`.
`char *thousands_sep`
`char *mon_thousands_sep`
  These are the separators used to delimit groups of digits to the left of the decimal point in formatting non-monetary and monetary quantities, respectively. In the ‘`C`’ locale, both members have a value of `""` (the empty string).
`char *grouping`
`char *mon_grouping`
  These are strings that specify how to group the digits to the left of the decimal point. `grouping` applies to non-monetary quantities and `mon_grouping` applies to monetary quantities. Use either `thousands_sep` or `mon_thousands_sep` to separate the digit groups. Each member of these strings is to be interpreted as an integer value of type `char`. Successive numbers (from left to right) give the sizes of successive groups (from right to left, starting at the decimal point.) The last member is either `0`, in which case the previous member is used over and over again for all the remaining groups, or `CHAR_MAX`, in which case there is no more grouping—or, put another way, any remaining digits form one large group without separators.

  For example, if `grouping` is `"\04\03\02"`, the correct grouping for the number `123456787654321` is ‘`12`’, ‘`34`’, ‘`56`’, ‘`78`’, ‘`765`’, ‘`4321`’. This uses a group of 4 digits at the end, preceded by a group of 3 digits, preceded by groups of 2 digits (as many as needed). With a separator of ‘`,`’, the number would be printed as ‘`12,34,56,78,765,4321`’.

  A value of `"\03"` indicates repeated groups of three digits, as normally used in the U.S.

  In the standard ‘`C`’ locale, both `grouping` and `mon_grouping` have a value of `""`. This value specifies no grouping at all.

`char int_frac_digits`
`char frac_digits`
  These are small integers indicating how many fractional digits (to the right of the decimal point) should be displayed in a monetary value in international and local formats, respectively. (Most often, both members have the same value.)

  In the standard ‘`C`’ locale, both of these members have the value `CHAR_MAX`, meaning “unspecified”. The ISO standard doesn't say what to do when you find this value; we recommend printing no fractional digits. (This locale also specifies the empty string for `mon_decimal_point`, so printing any fractional digits would be confusing!)