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## 10.3 C++ Formatted Output

The following functions are provided in ‘`libgmpxx`’ (see section Headers and Libraries), which is built if C++ support is enabled (see section Build Options).
Prototypes are available from `<gmp.h>`

.

- Function:
*ostream&***operator<<***(ostream&*`stream`, const mpz_t`op`) Print

`op`to`stream`, using its`ios`

formatting settings.`ios::width`

is reset to 0 after output, the same as the standard`ostream operator<<`

routines do.In hex or octal,

`op`is printed as a signed number, the same as for decimal. This is unlike the standard`operator<<`

routines on`int`

etc, which instead give twos complement.

- Function:
*ostream&***operator<<***(ostream&*`stream`, const mpq_t`op`) Print

`op`to`stream`, using its`ios`

formatting settings.`ios::width`

is reset to 0 after output, the same as the standard`ostream operator<<`

routines do.Output will be a fraction like ‘

`5/9`’, or if the denominator is 1 then just a plain integer like ‘`123`’.In hex or octal,

`op`is printed as a signed value, the same as for decimal. If`ios::showbase`

is set then a base indicator is shown on both the numerator and denominator (if the denominator is required).

- Function:
*ostream&***operator<<***(ostream&*`stream`, const mpf_t`op`) Print

`op`to`stream`, using its`ios`

formatting settings.`ios::width`

is reset to 0 after output, the same as the standard`ostream operator<<`

routines do.The decimal point follows the standard library float

`operator<<`

, which on recent systems means the`std::locale`

imbued on`stream`.Hex and octal are supported, unlike the standard

`operator<<`

on`double`

. The mantissa will be in hex or octal, the exponent will be in decimal. For hex the exponent delimiter is an ‘`@`’. This is as per`mpf_out_str`

.`ios::showbase`

is supported, and will put a base on the mantissa, for example hex ‘`0x1.8`’ or ‘`0x0.8`’, or octal ‘`01.4`’ or ‘`00.4`’. This last form is slightly strange, but at least differentiates itself from decimal.

These operators mean that GMP types can be printed in the usual C++ way, for example,

mpz_t z; int n; ... cout << "iteration " << n << " value " << z << "\n";

But note that `ostream`

output (and `istream`

input, see section C++ Formatted Input) is the only overloading available for the GMP types and that
for instance using `+`

with an `mpz_t`

will have unpredictable
results. For classes with overloading, see C++ Class Interface.

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