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3 ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). |
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38 ** $QT_END_LICENSE$ |
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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \page qt4-tulip.html |
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44 \title The Tulip Container Classes |
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45 |
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46 \contentspage {What's New in Qt 4}{Home} |
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47 \previouspage What's New in Qt 4 |
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48 \nextpage The Interview Framework |
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49 |
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50 Qt 4 introduces a new set of containers that supersede both the old |
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51 QCollection pointer-based containers and the newer QTL value-based |
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52 containers. |
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53 |
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54 \tableofcontents |
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55 |
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56 \section1 General Overview |
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57 |
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58 The Tulip containers are similar to Qt 3's QTL containers |
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59 (QValueList, QValueVector, QMap), but have the following |
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60 advantages: |
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61 |
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62 \list |
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63 \o The containers provide new iterators with a nicer, less |
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64 error-prone syntax than STL, inspired by Java's iterators. (The |
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65 STL-style iterators are still available as a lightweight, |
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66 STL-compatible alternative.) |
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67 |
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68 \o The containers have been optimized for minimal code expansion. |
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69 |
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70 \o An empty container performs no memory allocation, and only |
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71 requires the same space as a pointer. |
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72 |
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73 \o Even though they are implicitly shared, they can safely be copied |
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74 across different threads without formality. There's no need to use |
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75 \c QDeepCopy. |
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76 \endlist |
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77 |
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78 Tulip provides the following sequential containers: QList, |
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79 QLinkedList, QVector, QStack, and QQueue. For most |
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80 applications, QList is the best type to use. Although it is |
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81 implemented as an array-list, it provides very fast prepends and |
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82 appends. If you really need a linked-list, use QLinkedList; if you |
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83 want your items to occupy consecutive memory locations, use QVector. |
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84 QStack and QQueue are convenience classes that provide LIFO and |
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85 FIFO semantics. |
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86 |
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87 Tulip also provides these associative containers: QMap, |
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88 QMultiMap, QHash, QMultiHash, and QSet. The "Multi" containers |
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89 conveniently support multiple values associated with a single |
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90 key. The "Hash" containers provide faster lookup by using a hash |
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91 function instead of a binary search on a sorted set. |
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92 |
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93 The Tulip containers support the \l foreach keyword, a Qt-specific |
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94 addition to the C++ language that is implemented using the standard |
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95 C++ preprocessor. The syntax is: |
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96 |
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97 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 0 |
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98 |
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99 Example: |
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100 |
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101 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 1 |
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102 |
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103 The iterator variable can also be defined outside the loop. For |
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104 example: |
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105 |
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106 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 2 |
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107 |
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108 Just like standard \c for loops, foreach supports braces, \c |
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109 break, \c continue, and nested loops. Qt makes a copy of the |
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110 container when it enters the loop. If you modify the container as |
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111 you are iterating, that won't affect the loop. |
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112 |
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113 For details about the new containers, see the |
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114 \l{Generic Containers} and \l{Generic Algorithms} overview documents. |
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115 |
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116 In addition to the new containers, considerable work has also gone into |
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117 QByteArray and QString. The Qt 3 QCString class has been |
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118 merged with QByteArray. The new QByteArray automatically provides |
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119 a '\0' terminator after the last character. For example, the byte array |
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120 of size 5 containing "abcde" has a null byte at position 5 (one past |
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121 the end). This solves all the typical problems that occurred in Qt 3 |
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122 with conversions between QByteArray and QCString. |
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123 |
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124 To avoid crashes, QByteArray::data() never returns a null |
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125 pointer. Furthermore, the distinction between null and empty |
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126 strings has been watered down so that \c{QByteArray() == |
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127 QByteArray("")} and \c{QString() == QString("")}. |
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128 |
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129 \section1 Examples |
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130 |
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131 The first group of examples show how to use the new Java-style |
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132 iterators. The main difference between the Java-style iterators and the |
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133 STL-style iterators is that the Java-style ones point between items (or |
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134 before the first item, or after the last item), whereas the STL ones |
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135 point at an item (or past the last item). One advantage of the |
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136 Java-style iterators is that iterating forward and backward are |
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137 symmetric operations. |
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138 |
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139 Traversing a container using a Java-style iterator: |
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140 |
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141 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 3 |
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142 |
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143 Modifying items using a Java-style iterator: |
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144 |
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145 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 4 |
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146 |
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147 Removing items using a Java-style iterator: |
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148 |
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149 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 5 |
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150 |
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151 Iterating over items with a particular value using STL-style vs. |
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152 Java-style iterators: |
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153 |
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154 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 6 |
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155 |
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156 Modifying and removing items using STL-style vs. Java-style |
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157 iterators: |
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158 |
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159 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 7 |
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160 |
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161 The next group of examples show the API of the container classes |
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162 themselves. The API is similar to the QTL classes of Qt 3, but is nicer |
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163 in many respects. |
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164 |
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165 Iterating over a QList using an index (which is fast even for large |
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166 lists, because QList is implemented as an array-list): |
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167 |
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168 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 8 |
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169 |
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170 Retrieving a value from a map, using a default value if the key |
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171 doesn't exist: |
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172 |
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173 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 9 |
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174 |
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175 Getting all the values for a particular key in a QMultiMap or QMultiHash: |
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176 |
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177 \snippet doc/src/snippets/code/doc_src_qt4-tulip.qdoc 10 |
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178 |
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179 \section1 Comparison with Qt 3 |
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180 |
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181 Tulip containers are value based. If you want to store a list where |
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182 each item is a QWidget *, use QList<QWidget *>. |
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183 |
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184 The new containers do not support auto-delete. In practice, we |
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185 discovered that the only case where auto-delete proved worthwhile was |
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186 when the data really should be stored as a value rather than as a |
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187 pointer (e.g., QList<int> rather than QList<int *>). If you need |
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188 to delete all the items in a container, use qDeleteAll(). |
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189 |
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190 If you use QValueList in Qt 3, you can replace it with either |
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191 QList or QLinkedList in Qt 4. In most cases, QList is the best |
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192 choice: It is typically faster, results in less code in your |
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193 executable, and requires less memory. However, QLinkedList's |
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194 iterators provide stronger guarantees, and only QLinkedList provides |
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195 constant-time insertions in the middle, which can make a difference for |
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196 lists with thousands of items. |
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197 |
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198 If you use QValueVector or QMap in Qt 3, the corresponding Qt 4 |
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199 classes (QVector, QMap) are very similar to use. |
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200 */ |