Re: [boost] io operations for stl containers?

From: Vladimir Prus (ghost_at_[hidden])
Date: 2003-02-04 03:22:19

Terje Slettebø wrote:
>>From: "Vladimir Prus" <ghost_at_[hidden]>
> 
> 
>>after having to output std::vector to stream again and again using custom
>>solution, I started to wonder why we don't have a solution in boost.
>>Does it makes sense to include operators<< for vectors, sets, etc?
[...]

>>and so on. There are basically two approaches:
>>
>>1. Operators use fixed format: bracked list with commas between values for
>>    vector, for example.
>>2. Manipulators are provided to set brackets and separators.
>>
>>I had implemented the second approach some time ago, but it turned out
>> that was overkill. So, 1) looks better now.
 >
> If this is done as a library, then I think it's best not to have hard-coded
> brackets and separators. One might use an xalloc() value for each type to
> output. For example something like:

You see, that's what I have implemented back in 2001. You could change 
braces/separator for each stl container, and it used xalloc()/pword().
There's one problem though: I don't remember the syntax of brace
changing, just because I used it a couple of times long ago and then
stopped. Probably, the scope should be more clearly defined:

Edward Diener wrote:
 > Al Stevens who writes the C++ column for "Doctor Dobbs Journal" put out a
 > persistent template library for C++ containers some time back. It is
 > probably on the DDJ web site, although I haven't looked there recently. You
 > might want to check that out and see what he did. I will readily admit I
 > have not had the need to persist container data in my daily programming but
 > I can understand others having that need.

Rozental, Gennadiy wrote:
 > I do not see a way how you could implement solution with better
 > flexibility/conciseness ratio than copy+ostream_iterator one.

I'm not much interested in persistence (after all, I hope that Robert's
library will take care of that). Likewise, I never needed arbitrary
delimiters, etc. But while developing an algorithm for finding k shortest
paths in a graph, I need to output each path, and have no easy standard way.
One might call this output operators are mostly debugging help, but why not
have standard debugging help?

> std::cout << boost::io_format<Map>(",", "[", "]") <<
> boost::io_format<MapList>("","","\n") << list << '\n';
> 
> This might print:
> 
> [1, a]
> [2, b]
> [3, c]

This example should one case where manipulators are desirable:

     vector< vector<int> > v;
     cout << v ;

Here, each nested vector better go on a separate line. I suggest:

     cout << multiline << v;

where "multiline" manipulator causes each element of the next output container
to go on separate line.

- Volodya