Numeric Input Conversions (The GNU C Library)

#### 12.14.4 Numeric Input Conversions ¶

This section describes the `scanf` conversions for reading numeric values.

The ‘`%d`’ conversion matches an optionally signed integer in decimal radix. The syntax that is recognized is the same as that for the `strtol` function (see Parsing of Integers) with the value `10` for the base argument.

The ‘`%i`’ conversion matches an optionally signed integer in any of the formats that the C language defines for specifying an integer constant. The syntax that is recognized is the same as that for the `strtol` function (see Parsing of Integers) with the value `0` for the base argument. (You can print integers in this syntax with `printf` by using the ‘`#`’ flag character with the ‘`%x`’, ‘`%o`’, ‘`%b`’, or ‘`%d`’ conversion. See Integer Conversions.)

For example, any of the strings ‘`10`’, ‘`0xa`’, or ‘`012`’ could be read in as integers under the ‘`%i`’ conversion. Each of these specifies a number with decimal value `10`.

The ‘`%b`’, ‘`%o`’, ‘`%u`’, and ‘`%x`’ conversions match unsigned integers in binary, octal, decimal, and hexadecimal radices, respectively. The syntax that is recognized is the same as that for the `strtoul` function (see Parsing of Integers) with the appropriate value (`2`, `8`, `10`, or `16`) for the base argument. The ‘`%b`’ conversion accepts an optional leading ‘`0b`’ or ‘`0B`’ in all standards modes.

The ‘`%X`’ conversion is identical to the ‘`%x`’ conversion. They both permit either uppercase or lowercase letters to be used as digits.

The default type of the corresponding argument for the `%d`, `%i`, and `%n` conversions is `int *`, and `unsigned int *` for the other integer conversions. You can use the following type modifiers to specify other sizes of integer:

‘`hh`’

  Specifies that the argument is a `signed char *` or `unsigned char *`.

  This modifier was introduced in ISO C99.

‘`h`’

  Specifies that the argument is a `short int *` or `unsigned short int *`.

‘`j`’

  Specifies that the argument is a `intmax_t *` or `uintmax_t *`.

  This modifier was introduced in ISO C99.

‘`l`’

  Specifies that the argument is a `long int *` or `unsigned long int *`. Two ‘`l`’ characters is like the ‘`L`’ modifier, below.

  If used with ‘`%c`’ or ‘`%s`’ the corresponding parameter is considered as a pointer to a wide character or wide character string respectively. This use of ‘`l`’ was introduced in Amendment 1 to ISO C90.

‘`ll`’
‘`L`’
‘`q`’

  Specifies that the argument is a `long long int *` or `unsigned long long int *`. (The `long long` type is an extension supported by the GNU C compiler. For systems that don’t provide extra-long integers, this is the same as `long int`.)

  The ‘`q`’ modifier is another name for the same thing, which comes from 4.4 BSD; a `long long int` is sometimes called a “quad” `int`.

‘`t`’

  Specifies that the argument is a `ptrdiff_t *`.

  This modifier was introduced in ISO C99.

‘`wn`’

  Specifies that the argument is an `intn_t *` or `int_leastn_t *` (which are the same type), or `uintn_t *` or `uint_leastn_t *` (which are the same type).

  This modifier was introduced in ISO C23.

‘`wfn`’

  Specifies that the argument is an `int_fastn_t *` or `uint_fastn_t *`.

  This modifier was introduced in ISO C23.

‘`z`’

  Specifies that the argument is a `size_t *`.

  This modifier was introduced in ISO C99.

All of the ‘`%e`’, ‘`%f`’, ‘`%g`’, ‘`%E`’, ‘`%F`’ and ‘`%G`’ input conversions are interchangeable. They all match an optionally signed floating point number, in the same syntax as for the `strtod` function (see Parsing of Floats).

For the floating-point input conversions, the default argument type is `float *`. (This is different from the corresponding output conversions, where the default type is `double`; remember that `float` arguments to `printf` are converted to `double` by the default argument promotions, but `float *` arguments are not promoted to `double *`.) You can specify other sizes of float using these type modifiers:

‘`l`’

  Specifies that the argument is of type `double *`.

‘`L`’

  Specifies that the argument is of type `long double *`.

For all the above number parsing formats there is an additional optional flag ‘`'`’. When this flag is given the `scanf` function expects the number represented in the input string to be formatted according to the grouping rules of the currently selected locale (see Generic Numeric Formatting Parameters).

If the `"C"` or `"POSIX"` locale is selected there is no difference. But for a locale which specifies values for the appropriate fields in the locale the input must have the correct form in the input. Otherwise the longest prefix with a correct form is processed.