How do I print a standard pair?

Krzysztof Żelechowski

21 Sep 2011 21 Sep '11

2:59 p.m.

The expression (cout << make_pair (0, 1)) gives me an error. Does Boost offer me a way to print a (rvalue) pair, as within an expression?

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Matheus Peschke de Azevedo

21 Sep 21 Sep

9:06 p.m.

New subject: RES: How do I print a standard pair?

Krzysztof, According to the C++ standard, the ostream output (cout and wcout) will only handle built-in types (e.g., int, char, double, etc). It's up to the developer implement how all other types will print to the output. See full rationale and details in Stroustrup, Bjarne TCPPPL 3rd Edition - 21.2.2 Output of Built In Types. In short, you'll have to define a global operator<< for type std::pair: template std::basic_ostream<CharType>& operator<< (std::basic_ostream<CharType>& o, std::pair mypair) { return o << "This is my way of printing a pair: first: " << mypair.first << " and second: " << mypair.second; } Be advised that types T and U must be either built-in types or types with defined operator<<. Cheers, Matheus -----Mensagem original----- De: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] Em nome de Krzysztof Zelechowski Enviada em: quarta-feira, 21 de setembro de 2011 11:59 Para: boost-users@lists.boost.org Assunto: [Boost-users] How do I print a standard pair? The expression (cout << make_pair (0, 1)) gives me an error. Does Boost offer me a way to print a (rvalue) pair, as within an expression? _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Krzysztof Żelechowski

26 Sep 26 Sep

7:51 a.m.

New subject: RES: How do I print a standard pair?

Matheus Peschke de Azevedo wrote:

...

Krzysztof,

According to the C++ standard, the ostream output (cout and wcout) will only handle built-in types (e.g., int, char, double, etc).

Not true, vide ::std:: complex.

...

It's up to the developer implement how all other types will print to the output. See full rationale and details in Stroustrup, Bjarne TCPPPL 3rd Edition - 21.2.2 Output of Built In Types.

In short, you'll have to define a global operator<< for type std::pair:

template std::basic_ostream<CharType>& operator<< (std::basic_ostream<CharType>& o, std::pair mypair) { return o << "This is my way of printing a pair: first: " << mypair.first << " and second: " << mypair.second; }

This is strictly forbidden by the standard AFAIK. Chris

Igor R

2:08 p.m.

New subject: RES: How do I print a standard pair?

...

...
In short, you'll have to define a global operator<< for type std::pair:

template std::basic_ostream<CharType>& operator<< (std::basic_ostream<CharType>& o, std::pair mypair) { return o << "This is my way of printing a pair: first: " << mypair.first << " and second: " << mypair.second; }

This is strictly forbidden by the standard AFAIK.

How can the standard forbid defining your own operators? The standard forbids putting things into std namespace.

Nathan Ridge

6:31 p.m.

New subject: RES: How do I print a standard pair?

...

...
It's up to the developer implement how all other types will print to the output. See full rationale and details in Stroustrup, Bjarne TCPPPL 3rd Edition - 21.2.2 Output of Built In Types.

In short, you'll have to define a global operator<< for type std::pair:

template std::basic_ostream<CharType>& operator<< (std::basic_ostream<CharType>& o, std::pair mypair) { return o << "This is my way of printing a pair: first: " << mypair.first << " and second: " << mypair.second; }

This is strictly forbidden by the standard AFAIK.

Chris

It's forbidden if the overload is placed inside namespace std. Placing it in a different namespace (including the global namespace) is perfectly OK, AFAIK. Nate

Boris Schaeling

27 Sep 27 Sep

10 p.m.

On Wed, 21 Sep 2011 16:59:06 +0200, Krzysztof Żelechowski wrote:

...

The expression (cout << make_pair (0, 1)) gives me an error. Does Boost offer me a way to print a (rvalue) pair, as within an expression?

If you can replace std::pair with boost::tuple, you could write (cout << make_tuple (0, 1)). Boris

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Boris Schaeling
Igor R
Krzysztof Żelechowski
Matheus Peschke de Azevedo
Nathan Ridge