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10.3 C++ Formatted Output

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

— Function: ostream& operator<< (ostream& stream, 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, 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, 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 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.