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`gmp_printf`

and friends accept format strings similar to the standard C
`printf`

(see Formatted Output in The GNU C
Library Reference Manual). A format specification is of the form

% [flags] [width] [.[precision]] [type] conv

GMP adds types ‘`Z`’, ‘`Q`’ and ‘`F`’ for `mpz_t`

, `mpq_t`

and `mpf_t`

respectively, ‘`M`’ for `mp_limb_t`

, and ‘`N`’ for
an `mp_limb_t`

array. ‘`Z`’, ‘`Q`’, ‘`M`’ and ‘`N`’ behave
like integers. ‘`Q`’ will print a ‘`/`’ and a denominator, if needed.
‘`F`’ behaves like a float. For example,

mpz_t z; gmp_printf ("%s is an mpz %Zd\n", "here", z); mpq_t q; gmp_printf ("a hex rational: %#40Qx\n", q); mpf_t f; int n; gmp_printf ("fixed point mpf %.*Ff with %d digits\n", n, f, n); mp_limb_t l; gmp_printf ("limb %Mu\n", l); const mp_limb_t *ptr; mp_size_t size; gmp_printf ("limb array %Nx\n", ptr, size);

For ‘`N`’ the limbs are expected least significant first, as per the
`mpn`

functions (see Low-level Functions). A negative size can be
given to print the value as a negative.

All the standard C `printf`

types behave the same as the C library
`printf`

, and can be freely intermixed with the GMP extensions. In the
current implementation the standard parts of the format string are simply
handed to `printf`

and only the GMP extensions handled directly.

The flags accepted are as follows. GLIBC style ‘`'`’ is only for the
standard C types (not the GMP types), and only if the C library supports it.

`0`

pad with zeros (rather than spaces) `#`

show the base with ‘ 0x’, ‘0X’ or ‘0’`+`

always show a sign (space) show a space or a ‘ -’ sign`'`

group digits, GLIBC style (not GMP types)

The optional width and precision can be given as a number within the format
string, or as a ‘`*`’ to take an extra parameter of type `int`

, the
same as the standard `printf`

.

The standard types accepted are as follows. ‘`h`’ and ‘`l`’ are
portable, the rest will depend on the compiler (or include files) for the type
and the C library for the output.

`h`

`short`

`hh`

`char`

`j`

`intmax_t`

or`uintmax_t`

`l`

`long`

or`wchar_t`

`ll`

`long long`

`L`

`long double`

`q`

`quad_t`

or`u_quad_t`

`t`

`ptrdiff_t`

`z`

`size_t`

The GMP types are

`F`

`mpf_t`

, float conversions`Q`

`mpq_t`

, integer conversions`M`

`mp_limb_t`

, integer conversions`N`

`mp_limb_t`

array, integer conversions`Z`

`mpz_t`

, integer conversions

The conversions accepted are as follows. ‘`a`’ and ‘`A`’ are always
supported for `mpf_t`

but depend on the C library for standard C float
types. ‘`m`’ and ‘`p`’ depend on the C library.

`a`

`A`

hex floats, C99 style `c`

character `d`

decimal integer `e`

`E`

scientific format float `f`

fixed point float `i`

same as `d`

`g`

`G`

fixed or scientific float `m`

`strerror`

string, GLIBC style`n`

store characters written so far `o`

octal integer `p`

pointer `s`

string `u`

unsigned integer `x`

`X`

hex integer

‘`o`’, ‘`x`’ and ‘`X`’ are unsigned for the standard C types, but for
types ‘`Z`’, ‘`Q`’ and ‘`N`’ they are signed. ‘`u`’ is not
meaningful for ‘`Z`’, ‘`Q`’ and ‘`N`’.

‘`M`’ is a proxy for the C library ‘`l`’ or ‘`L`’, according to the
size of `mp_limb_t`

. Unsigned conversions will be usual, but a signed
conversion can be used and will interpret the value as a twos complement
negative.

‘`n`’ can be used with any type, even the GMP types.

Other types or conversions that might be accepted by the C library
`printf`

cannot be used through `gmp_printf`

, this includes for
instance extensions registered with GLIBC `register_printf_function`

.
Also currently there’s no support for POSIX ‘`$`’ style numbered arguments
(perhaps this will be added in the future).

The precision field has its usual meaning for integer ‘`Z`’ and float
‘`F`’ types, but is currently undefined for ‘`Q`’ and should not be used
with that.

`mpf_t`

conversions only ever generate as many digits as can be
accurately represented by the operand, the same as `mpf_get_str`

does.
Zeros will be used if necessary to pad to the requested precision. This
happens even for an ‘`f`’ conversion of an `mpf_t`

which is an
integer, for instance *2^1024* in an `mpf_t`

of 128 bits
precision will only produce about 40 digits, then pad with zeros to the
decimal point. An empty precision field like ‘`%.Fe`’ or ‘`%.Ff`’ can
be used to specifically request just the significant digits. Without any dot
and thus no precision field, a precision value of 6 will be used. Note that
these rules mean that ‘`%Ff`’, ‘`%.Ff`’, and ‘`%.0Ff`’ will all be
different.

The decimal point character (or string) is taken from the current locale
settings on systems which provide `localeconv`

(see Locales
and Internationalization in The GNU C Library Reference Manual). The C
library will normally do the same for standard float output.

The format string is only interpreted as plain `char`

s, multibyte
characters are not recognised. Perhaps this will change in the future.

Next: Formatted Output Functions, Previous: Formatted Output, Up: Formatted Output [Index]