Real positional string formatting?

Question

^{(Note: I know of Boost.Format, I'm looking for a better way to do the following.)}
First a use-case example: In some countries, you name a person by calling his / her surname first and the forename last, while in other countries it's the exact opposite.

Now, for my code, I currently solve this with Boost.Format in the following fashion:

#include <boost/format.hpp>
#include <iostream>
#include <stdlib.h>
#include <utility>

int main(){
    using namespace boost;

    int pos1 = 2, pos2 = 1;
    char const* surname = "Surname", *forename = "Forename";

    // decision on ordering here
    bool some_condition = false;

    if(some_condition)
      std::swap(pos1,pos2);

    char buf[64];
    sprintf(buf,"Hello %c%d%c %c%d%c",'%',pos1,'%','%',pos2,'%');
    // buf == "Hello %[pos1]% %[pos2]%"; with [posN] = value of posN

    std::cout << format(buf) % surname % forename;
}

Now, I would rather have it like this, i.e., everything in the format line:

std::cout << format("Hello %%1%% %%2%%") % pos1 % pos2 % surname % forename;

But sadly, that doesn't work, as I get a nice parsing exception.

Is there any library to have real positional formatting? Or even a way to achieve this with Boost.Format that I don't know of?

Answer 1

In my opinion, Boost.Spirit.Karma is the definitive modern output formatting library.

Answer 2

This is the Message Formatting part of Boost.Locale which is similar to GNU gettext.

In it you would write:

cout << format(translate("Hello {1} {2}!")) % forename % surname << endl;

And then a translator would translate the string using message catalogs:

msgid "Hello {1} {2}!"
msgstr "こんにちは {2}-さん!"

Answer 3

I'd simply swap the values that you interpolating

std::swap(surname, forename)

That'll do the job. If you don't want to mess with them, have references:

const std::string& param1(bSwapThem? forename : surname);
const std::string& param2(bSwapThem? surname  : forename);

KISS

Answer 4

Sounds like something that should be in the system locale but it doesn't look like it's currently supported.

What about the simple way?

   if(some_condition)
      std::cout << surname << " " << forename;
   else
      std::cout << forename << " " << surname;

Answer 5

I would have used ?:

char const* surname = "Surname", *forename = "Forename";
bool swapFlag = (some_condition) ? true : false;

std::cout << "Hello " << (swapFlag ? surname : forename) << " " << (!swapFlag ? surname : forename) << std::endl;

Answer 6

You can do this by applying format recursively:

cout << format(str(format("%%%1%%% %%%2%%%") % pos1 % pos2)) % surname % forname;

However, I would recommend using something like GNU gettext instead.