Custom manipulator for class

Question

I'm trying to write a stream manipulator with arguments. I have class with 3 int's CDate(Year, Month, Day). So I need to make manipulator date_format(const char*). e.g. :

CDate a(2006, 5, 15);
cout <<"DATE IS : " << date_format("%Y-hello-%d-world-%m-something-%d%d") << a;

Output will be :

DATE IS : 2006-hello-15-world-5-something-1515

Guess i need to use that

ios_base & dummy_date_format_manipulator ( ios_base & x )
{
    return x;
}

ios_base & ( * ( date_format ( const char * fmt ) ) )( ios_base & x )
{
    return dummy_date_format_manipulator;
}

but i don't know how.

Answer 1

You can use pword array for this. Every iostream in C++ has two arrays associated with it.

ios_base::iword - array of ints
ios_base::pword - array of void* pointers

You can store you own data in it. To obtain an index, that refers to an empty element in all iword and pword arrays you should use function std::ios_base::xalloc(). It returns int that you can use as an unique index in *word. You should obtain that index once on the start-up, and than use it for all operations with *word.

Then programming your own manip will look like:

Manipulator function, that receives reference to ios_base object and pointer to the format string, simply stores that pointer in pword

iosObject.pword(index_from_xalloc) = formatString

Then overloaded operator << (>>) obtains format string from the iostream object in the same way. After that you just make a conversion referencing to the format.