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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. static int formatId = ios_base::xalloc();
  5.  
  6. ostream & toFoo(ostream & stream) {
  7.   stream.iword(formatId) = 1;
  8.   return stream;
  9. }
  10. ostream & toBar(ostream & stream) {
  11.   stream.iword(formatId) = 2;
  12.   return stream;
  13. }
  14.  
  15. struct FooBar {};
  16.  
  17. ostream & operator<<(ostream & stream, FooBar const &) {
  18.   switch (stream.iword(formatId)) {
  19.     case 1: stream << "foo"; break;
  20.     case 2: stream << "bar"; break;
  21.     default: stream << "wild foobar";
  22.   }
  23.   return stream;
  24. }
  25.  
  26. int main() {
  27.   FooBar f;
  28.   cout << f << toFoo << " " << f << endl;
  29.   cout << f << toBar << " " << f << endl;
  30.   cout << f << endl;
  31.   return 0;
  32. }
Success #stdin #stdout 0s 3456KB
comments (?)
stdin
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Standard input is empty
stdout
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wild foobar foo
foo bar
bar
https://ideone.com/BEynhV
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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