C++ What is the % operator doing here?

Question

I recently encountered code similar to this:

std::string myString = "test";
boost::format fmt("%s");

fmt % myString;

What is the (second) % operator doing here?

EDIT:

I understand the end result, but I could not find a definition of how the % operator can be used like this.

Can someone provide an example that explains what exactly the meaning of the % operator is here?

http://stackoverflow.com/questions/4421706/operator-overloading — StoryTeller - Unslander Monica, May 21 '13 at 23:38
Is the operator overridden by std::string, or by the type of boost::format? — mclaassen, May 21 '13 at 23:40
It's the syntax. `%` is overloaded. It does nothing with modulos and other things. — gkovacs90, May 21 '13 at 23:40
Ok, I understand what operator overloading is. I understand that % is normally used for modulus. Does anybody know whether % is being overriden by std::string here or by the type of boost::format? — mclaassen, May 21 '13 at 23:42
It looks similar to the way Python (at least Python 2) uses `%` for the equivalent of `sprintf`, [documented here](http://docs.python.org/2/library/stdtypes.html#string-formatting). I presume the `%` symbol was chosen as a mnemonic because of that character's use in format strings. — Keith Thompson, May 21 '13 at 23:43

score 3 · Accepted Answer · answered May 21 '13 at 23:40

I understand the end result, but I could not find a definition of how the % operator can be used like this.

template<class T>  
basic_format&   operator%(const T& x)
    { return io::detail::feed<CharT, Tr, Alloc, const T&>(*this,x); }

This member function gets invoked whenever you use the code fmt % value where fmt is of type boost::basic_format<Ch>.

score 1 · Answer 2 · edited May 22 '13 at 00:17

1

% is an overloaded operator. Click here.

edited May 22 '13 at 00:17

David G

answered May 21 '13 at 23:39

Mou

2 Answers2