base/string_tokenizer.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_STRING_TOKENIZER_H_
   6 #define BASE_STRING_TOKENIZER_H_
   7 #pragma once
   8
   9 #include <algorithm>
  10 #include <string>
  11
  12 #include "base/string_piece.h"
  13
  14 // StringTokenizerT is a simple string tokenizer class.  It works like an
  15 // iterator that with each step (see the Advance method) updates members that
  16 // refer to the next token in the input string.  The user may optionally
  17 // configure the tokenizer to return delimiters.
  18 //
  19 // Warning: be careful not to pass a C string into the 2-arg constructor:
  20 // StringTokenizer t("this is a test", " ");  // WRONG
  21 // This will create a temporary std::string, save the begin() and end()
  22 // iterators, and then the string will be freed before we actually start
  23 // tokenizing it.
  24 // Instead, use a std::string or use the 3 arg constructor of CStringTokenizer.
  25 //
  26 //
  27 // EXAMPLE 1:
  28 //
  29 //   char input[] = "this is a test";
  30 //   CStringTokenizer t(input, input + strlen(input), " ");
  31 //   while (t.GetNext()) {
  32 //     printf("%s\n", t.token().c_str());
  33 //   }
  34 //
  35 // Output:
  36 //
  37 //   this
  38 //   is
  39 //   a
  40 //   test
  41 //
  42 //
  43 // EXAMPLE 2:
  44 //
  45 //   std::string input = "no-cache=\"foo, bar\", private";
  46 //   StringTokenizer t(input, ", ");
  47 //   t.set_quote_chars("\"");
  48 //   while (t.GetNext()) {
  49 //     printf("%s\n", t.token().c_str());
  50 //   }
  51 //
  52 // Output:
  53 //
  54 //   no-cache="foo, bar"
  55 //   private
  56 //
  57 //
  58 // EXAMPLE 3:
  59 //
  60 //   bool next_is_option = false, next_is_value = false;
  61 //   std::string input = "text/html; charset=UTF-8; foo=bar";
  62 //   StringTokenizer t(input, "; =");
  63 //   t.set_options(StringTokenizer::RETURN_DELIMS);
  64 //   while (t.GetNext()) {
  65 //     if (t.token_is_delim()) {
  66 //       switch (*t.token_begin()) {
  67 //         case ';':
  68 //           next_is_option = true;
  69 //           break;
  70 //         case '=':
  71 //           next_is_value = true;
  72 //           break;
  73 //       }
  74 //     } else {
  75 //       const char* label;
  76 //       if (next_is_option) {
  77 //         label = "option-name";
  78 //         next_is_option = false;
  79 //       } else if (next_is_value) {
  80 //         label = "option-value";
  81 //         next_is_value = false;
  82 //       } else {
  83 //         label = "mime-type";
  84 //       }
  85 //       printf("%s: %s\n", label, t.token().c_str());
  86 //     }
  87 //   }
  88 //
  89 //
  90 template <class str, class const_iterator>
  91 class StringTokenizerT {
  92  public:
  93   typedef typename str::value_type char_type;
  94
  95   // Options that may be pass to set_options()
  96   enum {
  97     // Specifies the delimiters should be returned as tokens
  98     RETURN_DELIMS = 1 << 0,
  99   };
 100
 101   // The string object must live longer than the tokenizer.  (In particular this
 102   // should not be constructed with a temporary.)
 103   StringTokenizerT(const str& string,
 104                    const str& delims) {
 105     Init(string.begin(), string.end(), delims);
 106   }
 107
 108   StringTokenizerT(const_iterator string_begin,
 109                    const_iterator string_end,
 110                    const str& delims) {
 111     Init(string_begin, string_end, delims);
 112   }
 113
 114   // Set the options for this tokenizer.  By default, this is 0.
 115   void set_options(int options) { options_ = options; }
 116
 117   // Set the characters to regard as quotes.  By default, this is empty.  When
 118   // a quote char is encountered, the tokenizer will switch into a mode where
 119   // it ignores delimiters that it finds.  It switches out of this mode once it
 120   // finds another instance of the quote char.  If a backslash is encountered
 121   // within a quoted string, then the next character is skipped.
 122   void set_quote_chars(const str& quotes) { quotes_ = quotes; }
 123
 124   // Call this method to advance the tokenizer to the next delimiter.  This
 125   // returns false if the tokenizer is complete.  This method must be called
 126   // before calling any of the token* methods.
 127   bool GetNext() {
 128     if (quotes_.empty() && options_ == 0)
 129       return QuickGetNext();
 130     else
 131       return FullGetNext();
 132   }
 133
 134   // Start iterating through tokens from the beginning of the string.
 135   void Reset() {
 136     token_end_ = start_pos_;
 137   }
 138
 139   // Returns true if token is a delimiter.  When the tokenizer is constructed
 140   // with the RETURN_DELIMS option, this method can be used to check if the
 141   // returned token is actually a delimiter.
 142   bool token_is_delim() const { return token_is_delim_; }
 143
 144   // If GetNext() returned true, then these methods may be used to read the
 145   // value of the token.
 146   const_iterator token_begin() const { return token_begin_; }
 147   const_iterator token_end() const { return token_end_; }
 148   str token() const { return str(token_begin_, token_end_); }
 149   base::StringPiece token_piece() const {
 150     return base::StringPiece(&*token_begin_,
 151                              std::distance(token_begin_, token_end_));
 152   }
 153
 154  private:
 155   void Init(const_iterator string_begin,
 156             const_iterator string_end,
 157             const str& delims) {
 158     start_pos_ = string_begin;
 159     token_begin_ = string_begin;
 160     token_end_ = string_begin;
 161     end_ = string_end;
 162     delims_ = delims;
 163     options_ = 0;
 164     token_is_delim_ = false;
 165   }
 166
 167   // Implementation of GetNext() for when we have no quote characters. We have
 168   // two separate implementations because AdvanceOne() is a hot spot in large
 169   // text files with large tokens.
 170   bool QuickGetNext() {
 171     token_is_delim_ = false;
 172     for (;;) {
 173       token_begin_ = token_end_;
 174       if (token_end_ == end_)
 175         return false;
 176       ++token_end_;
 177       if (delims_.find(*token_begin_) == str::npos)
 178         break;
 179       // else skip over delimiter.
 180     }
 181     while (token_end_ != end_ && delims_.find(*token_end_) == str::npos)
 182       ++token_end_;
 183     return true;
 184   }
 185
 186   // Implementation of GetNext() for when we have to take quotes into account.
 187   bool FullGetNext() {
 188     AdvanceState state;
 189     token_is_delim_ = false;
 190     for (;;) {
 191       token_begin_ = token_end_;
 192       if (token_end_ == end_)
 193         return false;
 194       ++token_end_;
 195       if (AdvanceOne(&state, *token_begin_))
 196         break;
 197       if (options_ & RETURN_DELIMS) {
 198         token_is_delim_ = true;
 199         return true;
 200       }
 201       // else skip over delimiter.
 202     }
 203     while (token_end_ != end_ && AdvanceOne(&state, *token_end_))
 204       ++token_end_;
 205     return true;
 206   }
 207
 208   bool IsDelim(char_type c) const {
 209     return delims_.find(c) != str::npos;
 210   }
 211
 212   bool IsQuote(char_type c) const {
 213     return quotes_.find(c) != str::npos;
 214   }
 215
 216   struct AdvanceState {
 217     bool in_quote;
 218     bool in_escape;
 219     char_type quote_char;
 220     AdvanceState() : in_quote(false), in_escape(false), quote_char('\0') {}
 221   };
 222
 223   // Returns true if a delimiter was not hit.
 224   bool AdvanceOne(AdvanceState* state, char_type c) {
 225     if (state->in_quote) {
 226       if (state->in_escape) {
 227         state->in_escape = false;
 228       } else if (c == '\\') {
 229         state->in_escape = true;
 230       } else if (c == state->quote_char) {
 231         state->in_quote = false;
 232       }
 233     } else {
 234       if (IsDelim(c))
 235         return false;
 236       state->in_quote = IsQuote(state->quote_char = c);
 237     }
 238     return true;
 239   }
 240
 241   const_iterator start_pos_;
 242   const_iterator token_begin_;
 243   const_iterator token_end_;
 244   const_iterator end_;
 245   str delims_;
 246   str quotes_;
 247   int options_;
 248   bool token_is_delim_;
 249 };
 250
 251 typedef StringTokenizerT<std::string, std::string::const_iterator>
 252     StringTokenizer;
 253 typedef StringTokenizerT<std::wstring, std::wstring::const_iterator>
 254     WStringTokenizer;
 255 typedef StringTokenizerT<std::string, const char*> CStringTokenizer;
 256
 257 #endif  // BASE_STRING_TOKENIZER_H_