#include <iostream>
#include <iomanip>
#include <cassert>
#include "boost/format.hpp"
// 2 custom namespaces, to bring in a few useful names :
namespace MyNS_ForOutput {
using std::cout; using std::cerr;
using std::string;
using std::endl; using std::flush;
using boost::format;
using boost::io::group;
}
namespace MyNS_Manips {
using std::setfill;
using std::setw;
using std::hex ;
using std::dec ;
// gcc-2.95 doesnt define the next ones
// using std::showbase ;
// using std::left ;
// using std::right ;
// using std::internal ;
}
int main(){
using namespace MyNS_ForOutput;
using namespace MyNS_Manips;
std::cout << format("%|1$1| %|2$3|") % "Hello" % 3 << std::endl;
// Reordering :
cout << format("%1% %2% %3% %2% %1% \n") % "o" % "oo" % "O"; // 'simple' style.
// prints "o oo O oo o \n"
cout << format("(x,y) = (%1$+5d,%2$+5d) \n") % -23 % 35; // Posix-Printf style
// No reordering :
cout << format("writing %s, x=%s : %d-th step \n") % "toto" % 40.23 % 50;
// prints "writing toto, x=40.23 : 50-th step \n"
cout << format("(x,y) = (%+5d,%+5d) \n") % -23 % 35;
cout << format("(x,y) = (%|+5|,%|+5|) \n") % -23 % 35;
cout << format("(x,y) = (%|1$+5|,%|2$+5|) \n") % -23 % 35;
// all those are the same, it prints "(x,y) = ( -23, +35) \n"
// Using manipulators, via 'group' :
cout << format("%2% %1% %2%\n") % 1 % group(setfill('X'), hex, setw(4), 16+3) ;
// prints "XX13 1 XX13\n"
// printf directives's type-flag can be used to pass formatting options :
cout << format("_%1$4d_ is : _%1$#4x_, _%1$#4o_, and _%1$s_ by default\n") % 18;
// prints "_ 18_ is : _0x12_, _ 022_, and _18_ by default\n"
// Taking the string value :
std::string s;
s= str( format(" %d %d ") % 11 % 22 );
assert( s == " 11 22 ");
// -----------------------------------------------
// %% prints '%'
cout << format("%%##%#x ") % 20 << endl;
// prints "%##0x14 "
// -----------------------------------------------
// Enforcing the right number of arguments
// Too much arguments will throw an exception when feeding the unwanted argument :
try {
format(" %1% %1% ") % 101 % 102;
// the format-string refers to ONE argument, twice. not 2 arguments.
// thus giving 2 arguments is an error
}
catch (boost::io::too_many_args& exc) {
cerr << exc.what() << "\n\t\t***Dont worry, that was planned\n";
}
// Too few arguments when requesting the result will also throw an exception :
try {
cerr << format(" %|3$| ") % 101;
// even if %1$ and %2$ are not used, you should have given 3 arguments
}
catch (boost::io::too_few_args& exc) {
cerr << exc.what() << "\n\t\t***Dont worry, that was planned\n";
}
cerr << "\n\nEverything went OK, exiting. \n";
return 0;
}
输出：
Hello 3
o oo O oo o
(x,y) = ( -23, +35)
writing toto, x=40.23 : 50-th step
(x,y) = ( -23, +35)
(x,y) = ( -23, +35)
(x,y) = ( -23, +35)
XX13 1 XX13
_ 18_ is : _0x12_, _ 022_, and _18_ by default
%##0x14
boost::too_many_args: format-string refered to less arguments than were passed
***Dont worry, that was planned
boost::too_few_args: format-string refered to more arguments than were passed
***Dont worry, that was planned
Everything went OK, exiting.