icuSources/common/unicode/stringpiece.h

   1 // © 2016 and later: Unicode, Inc. and others.
   2 // License & terms of use: http://www.unicode.org/copyright.html
   3 // Copyright (C) 2009-2013, International Business Machines
   4 // Corporation and others. All Rights Reserved.
   5 //
   6 // Copyright 2001 and onwards Google Inc.
   7 // Author: Sanjay Ghemawat
   8
   9 // This code is a contribution of Google code, and the style used here is
  10 // a compromise between the original Google code and the ICU coding guidelines.
  11 // For example, data types are ICU-ified (size_t,int->int32_t),
  12 // and API comments doxygen-ified, but function names and behavior are
  13 // as in the original, if possible.
  14 // Assertion-style error handling, not available in ICU, was changed to
  15 // parameter "pinning" similar to UnicodeString.
  16 //
  17 // In addition, this is only a partial port of the original Google code,
  18 // limited to what was needed so far. The (nearly) complete original code
  19 // is in the ICU svn repository at icuhtml/trunk/design/strings/contrib
  20 // (see ICU ticket 6765, r25517).
  21
  22 #ifndef __STRINGPIECE_H__
  23 #define __STRINGPIECE_H__
  24
  25 /**
  26  * \file
  27  * \brief C++ API: StringPiece: Read-only byte string wrapper class.
  28  */
  29
  30 #include "unicode/utypes.h"
  31
  32 #if U_SHOW_CPLUSPLUS_API
  33
  34 #include <cstddef>
  35 #include <type_traits>
  36
  37 #include "unicode/uobject.h"
  38 #include "unicode/std_string.h"
  39
  40 // Arghh!  I wish C++ literals were "string".
  41
  42 U_NAMESPACE_BEGIN
  43
  44 /**
  45  * A string-like object that points to a sized piece of memory.
  46  *
  47  * We provide non-explicit singleton constructors so users can pass
  48  * in a "const char*" or a "string" wherever a "StringPiece" is
  49  * expected.
  50  *
  51  * Functions or methods may use StringPiece parameters to accept either a
  52  * "const char*" or a "string" value that will be implicitly converted to a
  53  * StringPiece.
  54  *
  55  * Systematic usage of StringPiece is encouraged as it will reduce unnecessary
  56  * conversions from "const char*" to "string" and back again.
  57  *
  58  * @stable ICU 4.2
  59  */
  60 class U_COMMON_API StringPiece : public UMemory {
  61  private:
  62   const char*   ptr_;
  63   int32_t       length_;
  64
  65  public:
  66   /**
  67    * Default constructor, creates an empty StringPiece.
  68    * @stable ICU 4.2
  69    */
  70   StringPiece() : ptr_(NULL), length_(0) { }
  71   /**
  72    * Constructs from a NUL-terminated const char * pointer.
  73    * @param str a NUL-terminated const char * pointer
  74    * @stable ICU 4.2
  75    */
  76   StringPiece(const char* str);
  77   /**
  78    * Constructs from a std::string.
  79    * @stable ICU 4.2
  80    */
  81   StringPiece(const std::string& str)
  82     : ptr_(str.data()), length_(static_cast<int32_t>(str.size())) { }
  83 #ifndef U_HIDE_DRAFT_API
  84   /**
  85    * Constructs from some other implementation of a string piece class, from any
  86    * C++ record type that has these two methods:
  87    *
  88    * \code{.cpp}
  89    *
  90    *   struct OtherStringPieceClass {
  91    *     const char* data();
  92    *     size_t size();
  93    *   };
  94    *
  95    * \endcode
  96    *
  97    * The other string piece class will typically be std::string_view from C++17
  98    * or absl::string_view from Abseil.
  99    *
 100    * @param str the other string piece
 101    * @draft ICU 65
 102    */
 103   template <typename T,
 104             typename = typename std::enable_if<
 105                 std::is_same<decltype(T().data()), const char*>::value &&
 106                 std::is_same<decltype(T().size()), size_t>::value>::type>
 107   StringPiece(T str)
 108       : ptr_(str.data()), length_(static_cast<int32_t>(str.size())) {}
 109 #endif  // U_HIDE_DRAFT_API
 110   /**
 111    * Constructs from a const char * pointer and a specified length.
 112    * @param offset a const char * pointer (need not be terminated)
 113    * @param len the length of the string; must be non-negative
 114    * @stable ICU 4.2
 115    */
 116   StringPiece(const char* offset, int32_t len) : ptr_(offset), length_(len) { }
 117   /**
 118    * Substring of another StringPiece.
 119    * @param x the other StringPiece
 120    * @param pos start position in x; must be non-negative and <= x.length().
 121    * @stable ICU 4.2
 122    */
 123   StringPiece(const StringPiece& x, int32_t pos);
 124   /**
 125    * Substring of another StringPiece.
 126    * @param x the other StringPiece
 127    * @param pos start position in x; must be non-negative and <= x.length().
 128    * @param len length of the substring;
 129    *            must be non-negative and will be pinned to at most x.length() - pos.
 130    * @stable ICU 4.2
 131    */
 132   StringPiece(const StringPiece& x, int32_t pos, int32_t len);
 133
 134   /**
 135    * Returns the string pointer. May be NULL if it is empty.
 136    *
 137    * data() may return a pointer to a buffer with embedded NULs, and the
 138    * returned buffer may or may not be null terminated.  Therefore it is
 139    * typically a mistake to pass data() to a routine that expects a NUL
 140    * terminated string.
 141    * @return the string pointer
 142    * @stable ICU 4.2
 143    */
 144   const char* data() const { return ptr_; }
 145   /**
 146    * Returns the string length. Same as length().
 147    * @return the string length
 148    * @stable ICU 4.2
 149    */
 150   int32_t size() const { return length_; }
 151   /**
 152    * Returns the string length. Same as size().
 153    * @return the string length
 154    * @stable ICU 4.2
 155    */
 156   int32_t length() const { return length_; }
 157   /**
 158    * Returns whether the string is empty.
 159    * @return TRUE if the string is empty
 160    * @stable ICU 4.2
 161    */
 162   UBool empty() const { return length_ == 0; }
 163
 164   /**
 165    * Sets to an empty string.
 166    * @stable ICU 4.2
 167    */
 168   void clear() { ptr_ = NULL; length_ = 0; }
 169
 170   /**
 171    * Reset the stringpiece to refer to new data.
 172    * @param xdata pointer the new string data.  Need not be nul terminated.
 173    * @param len the length of the new data
 174    * @stable ICU 4.8
 175    */
 176   void set(const char* xdata, int32_t len) { ptr_ = xdata; length_ = len; }
 177
 178   /**
 179    * Reset the stringpiece to refer to new data.
 180    * @param str a pointer to a NUL-terminated string.
 181    * @stable ICU 4.8
 182    */
 183   void set(const char* str);
 184
 185   /**
 186    * Removes the first n string units.
 187    * @param n prefix length, must be non-negative and <=length()
 188    * @stable ICU 4.2
 189    */
 190   void remove_prefix(int32_t n) {
 191     if (n >= 0) {
 192       if (n > length_) {
 193         n = length_;
 194       }
 195       ptr_ += n;
 196       length_ -= n;
 197     }
 198   }
 199
 200   /**
 201    * Removes the last n string units.
 202    * @param n suffix length, must be non-negative and <=length()
 203    * @stable ICU 4.2
 204    */
 205   void remove_suffix(int32_t n) {
 206     if (n >= 0) {
 207       if (n <= length_) {
 208         length_ -= n;
 209       } else {
 210         length_ = 0;
 211       }
 212     }
 213   }
 214
 215   /**
 216    * Maximum integer, used as a default value for substring methods.
 217    * @stable ICU 4.2
 218    */
 219   static const int32_t npos; // = 0x7fffffff;
 220
 221   /**
 222    * Returns a substring of this StringPiece.
 223    * @param pos start position; must be non-negative and <= length().
 224    * @param len length of the substring;
 225    *            must be non-negative and will be pinned to at most length() - pos.
 226    * @return the substring StringPiece
 227    * @stable ICU 4.2
 228    */
 229   StringPiece substr(int32_t pos, int32_t len = npos) const {
 230     return StringPiece(*this, pos, len);
 231   }
 232 };
 233
 234 /**
 235  * Global operator == for StringPiece
 236  * @param x The first StringPiece to compare.
 237  * @param y The second StringPiece to compare.
 238  * @return TRUE if the string data is equal
 239  * @stable ICU 4.8
 240  */
 241 U_EXPORT UBool U_EXPORT2
 242 operator==(const StringPiece& x, const StringPiece& y);
 243
 244 /**
 245  * Global operator != for StringPiece
 246  * @param x The first StringPiece to compare.
 247  * @param y The second StringPiece to compare.
 248  * @return TRUE if the string data is not equal
 249  * @stable ICU 4.8
 250  */
 251 inline UBool operator!=(const StringPiece& x, const StringPiece& y) {
 252   return !(x == y);
 253 }
 254
 255 U_NAMESPACE_END
 256
 257 #endif /* U_SHOW_CPLUSPLUS_API */
 258
 259 #endif  // __STRINGPIECE_H__