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  1. #include <iostream>
  2. #include <iomanip>
  3. #include <map>
  4. #include <string>
  5.  
  6. enum token_t
  7. {
  8.   END,
  9.   PLUS,
  10.   NUMBER,
  11.   D,
  12.   DR,
  13.   R,
  14.   A,
  15.  
  16.   // ...
  17. };
  18.  
  19. // ...
  20.  
  21. using keyword_to_token_t = std::map < std::string, token_t >;
  22.  
  23. keyword_to_token_t kwtt =
  24. {
  25.   {"A", A},
  26.   {"D", D},
  27.   {"R", R},
  28.   {"DR", DR}
  29.  
  30.   // ...
  31.  
  32. };
  33.  
  34. // ...
  35.  
  36. std::string s;
  37. int n;
  38.  
  39. // ...
  40.  
  41. token_t get_token( std::istream& is )
  42. {
  43.   char c;
  44.  
  45.   std::ws( is ); // discard white-space
  46.  
  47.   if ( !is.get( c ) ) // read a character
  48.     return END; // failed to read or eof
  49.  
  50.   // analyze the character
  51.   switch ( c )
  52.   {
  53.   case '+': // simple token
  54.     return PLUS;
  55.  
  56.   case '0': case '1': // rest of digits
  57.     is.putback( c ); // it starts with a digit: it must be a number, so put it back 
  58.     is >> n; // and let the library to the hard work
  59.     return NUMBER;
  60.     //...
  61.  
  62.   default: // keyword
  63.     is.putback( c );
  64.     is >> s;
  65.     if ( kwtt.find( s ) == kwtt.end() )
  66.       throw "keyword not found";
  67.     return kwtt[ s ];
  68.   }
  69. }
  70.  
  71. int main()
  72. {
  73.   try
  74.   {
  75.     while ( get_token( std::cin ) )
  76.       ;
  77.     std::cout << "valid tokens";
  78.   }
  79.   catch ( const char* e )
  80.   {
  81.     std::cout << e;
  82.   }
  83. }
  84.  
Success #stdin #stdout 0s 4512KB
comments (?)
stdin
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D DR R + A
stdout
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valid tokens
https://ideone.com/yuP3KV
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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