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1 /**************************************************************************** |
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2 ** |
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3 ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). |
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4 ** All rights reserved. |
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5 ** Contact: Nokia Corporation (qt-info@nokia.com) |
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6 ** |
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7 ** This file is part of the QtCore module of the Qt Toolkit. |
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8 ** |
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9 ** $QT_BEGIN_LICENSE:LGPL$ |
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10 ** No Commercial Usage |
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11 ** This file contains pre-release code and may not be distributed. |
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12 ** You may use this file in accordance with the terms and conditions |
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13 ** contained in the Technology Preview License Agreement accompanying |
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14 ** this package. |
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15 ** |
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16 ** GNU Lesser General Public License Usage |
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17 ** Alternatively, this file may be used under the terms of the GNU Lesser |
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18 ** General Public License version 2.1 as published by the Free Software |
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19 ** Foundation and appearing in the file LICENSE.LGPL included in the |
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20 ** packaging of this file. Please review the following information to |
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21 ** ensure the GNU Lesser General Public License version 2.1 requirements |
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22 ** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. |
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23 ** |
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24 ** In addition, as a special exception, Nokia gives you certain additional |
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25 ** rights. These rights are described in the Nokia Qt LGPL Exception |
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26 ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. |
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27 ** |
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28 ** If you have questions regarding the use of this file, please contact |
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29 ** Nokia at qt-info@nokia.com. |
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30 ** |
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31 ** |
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32 ** |
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33 ** |
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34 ** |
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35 ** |
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36 ** |
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37 ** |
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38 ** $QT_END_LICENSE$ |
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39 ** |
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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \class QPointer |
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44 \brief The QPointer class is a template class that provides guarded pointers to QObjects. |
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45 |
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46 \ingroup objectmodel |
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47 |
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48 |
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49 A guarded pointer, QPointer<T>, behaves like a normal C++ |
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50 pointer \c{T *}, except that it is automatically set to 0 when the |
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51 referenced object is destroyed (unlike normal C++ pointers, which |
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52 become "dangling pointers" in such cases). \c T must be a |
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53 subclass of QObject. |
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54 |
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55 Guarded pointers are useful whenever you need to store a pointer |
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56 to a QObject that is owned by someone else, and therefore might be |
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57 destroyed while you still hold a reference to it. You can safely |
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58 test the pointer for validity. |
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59 |
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60 Qt also provides QSharedPointer, an implementation of a reference-counted |
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61 shared pointer object, which can be used to maintain a collection of |
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62 references to an individual pointer. |
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63 |
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64 Example: |
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65 |
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66 \snippet doc/src/snippets/pointer/pointer.cpp 0 |
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67 \dots |
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68 \snippet doc/src/snippets/pointer/pointer.cpp 1 |
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69 \snippet doc/src/snippets/pointer/pointer.cpp 2 |
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70 |
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71 If the QLabel is deleted in the meantime, the \c label variable |
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72 will hold 0 instead of an invalid address, and the last line will |
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73 never be executed. |
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74 |
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75 The functions and operators available with a QPointer are the |
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76 same as those available with a normal unguarded pointer, except |
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77 the pointer arithmetic operators (\c{+}, \c{-}, \c{++}, and |
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78 \c{--}), which are normally used only with arrays of objects. |
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79 |
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80 Use QPointers like normal pointers and you will not need to read |
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81 this class documentation. |
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82 |
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83 For creating guarded pointers, you can construct or assign to them |
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84 from a T* or from another guarded pointer of the same type. You |
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85 can compare them with each other using operator==() and |
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86 operator!=(), or test for 0 with isNull(). You can dereference |
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87 them using either the \c *x or the \c x->member notation. |
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88 |
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89 A guarded pointer will automatically cast to a \c T *, so you can |
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90 freely mix guarded and unguarded pointers. This means that if you |
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91 have a QPointer<QWidget>, you can pass it to a function that |
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92 requires a QWidget *. For this reason, it is of little value to |
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93 declare functions to take a QPointer as a parameter; just use |
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94 normal pointers. Use a QPointer when you are storing a pointer |
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95 over time. |
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96 |
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97 Note that class \c T must inherit QObject, or a compilation or |
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98 link error will result. |
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99 |
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100 \sa QSharedPointer, QObject, QObjectCleanupHandler |
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101 */ |
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102 |
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103 /*! |
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104 \fn QPointer::QPointer() |
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105 |
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106 Constructs a 0 guarded pointer. |
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107 |
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108 \sa isNull() |
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109 */ |
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110 |
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111 /*! |
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112 \fn QPointer::QPointer(T* p) |
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113 |
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114 Constructs a guarded pointer that points to same object that \a p |
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115 points to. |
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116 */ |
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117 |
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118 /*! |
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119 \fn QPointer::QPointer(const QPointer<T> &p) |
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120 |
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121 Copies one guarded pointer from another. The constructed guarded |
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122 pointer points to the same object that \a p points to (which may |
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123 be 0). |
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124 */ |
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125 |
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126 /*! |
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127 \fn QPointer::~QPointer() |
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128 |
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129 Destroys the guarded pointer. Just like a normal pointer, |
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130 destroying a guarded pointer does \e not destroy the object being |
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131 pointed to. |
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132 */ |
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133 |
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134 /*! |
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135 \fn QPointer<T>& QPointer::operator=(const QPointer<T> &p) |
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136 |
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137 Assignment operator. This guarded pointer will now point to the |
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138 same object that \a p points to. |
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139 */ |
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140 |
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141 /*! |
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142 \fn QPointer<T> & QPointer::operator=(T* p) |
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143 |
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144 Assignment operator. This guarded pointer will now point to the |
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145 same object that \a p points to. |
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146 */ |
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147 |
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148 /*! |
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149 \fn T* QPointer::data() const |
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150 \since 4.4 |
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151 |
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152 Returns the pointer to the object being guarded. |
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153 */ |
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154 |
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155 /*! |
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156 \fn bool QPointer::isNull() const |
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157 |
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158 Returns \c true if the referenced object has been destroyed or if |
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159 there is no referenced object; otherwise returns false. |
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160 */ |
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161 |
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162 /*! |
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163 \fn T* QPointer::operator->() const |
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164 |
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165 Overloaded arrow operator; implements pointer semantics. Just use |
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166 this operator as you would with a normal C++ pointer. |
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167 */ |
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168 |
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169 /*! |
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170 \fn T& QPointer::operator*() const |
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171 |
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172 Dereference operator; implements pointer semantics. Just use this |
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173 operator as you would with a normal C++ pointer. |
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174 */ |
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175 |
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176 /*! |
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177 \fn QPointer::operator T*() const |
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178 |
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179 Cast operator; implements pointer semantics. Because of this |
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180 function you can pass a QPointer\<T\> to a function where a T* |
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181 is required. |
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182 */ |
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183 |
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184 /*! |
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185 \fn bool operator==(const T *o, const QPointer<T> &p) |
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186 |
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187 Equality operator. Returns true if \a o and the guarded |
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188 pointer \a p are pointing to the same object, otherwise |
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189 returns false. |
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190 |
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191 */ |
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192 /*! |
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193 \fn bool operator==(const QPointer<T> &p, const T *o) |
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194 |
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195 Equality operator. Returns true if \a o and the guarded |
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196 pointer \a p are pointing to the same object, otherwise |
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197 returns false. |
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198 |
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199 */ |
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200 /*! |
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201 \fn bool operator==(T *o, const QPointer<T> &p) |
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202 |
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203 Equality operator. Returns true if \a o and the guarded |
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204 pointer \a p are pointing to the same object, otherwise |
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205 returns false. |
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206 |
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207 */ |
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208 /*! |
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209 \fn bool operator==(const QPointer<T> &p, T *o) |
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210 |
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211 Equality operator. Returns true if \a o and the guarded |
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212 pointer \a p are pointing to the same object, otherwise |
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213 returns false. |
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214 |
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215 */ |
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216 /*! |
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217 \fn bool operator==(const QPointer<T> &p1, const QPointer<T> &p2) |
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218 |
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219 Equality operator. Returns true if the guarded pointers \a p1 and \a p2 |
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220 are pointing to the same object, otherwise |
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221 returns false. |
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222 |
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223 */ |
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224 |
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225 |
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226 /*! |
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227 \fn bool operator!=(const T *o, const QPointer<T> &p) |
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228 |
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229 Inequality operator. Returns true if \a o and the guarded |
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230 pointer \a p are not pointing to the same object, otherwise |
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231 returns false. |
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232 */ |
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233 /*! |
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234 \fn bool operator!=(const QPointer<T> &p, const T *o) |
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235 |
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236 Inequality operator. Returns true if \a o and the guarded |
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237 pointer \a p are not pointing to the same object, otherwise |
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238 returns false. |
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239 */ |
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240 /*! |
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241 \fn bool operator!=(T *o, const QPointer<T> &p) |
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242 |
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243 Inequality operator. Returns true if \a o and the guarded |
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244 pointer \a p are not pointing to the same object, otherwise |
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245 returns false. |
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246 */ |
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247 /*! |
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248 \fn bool operator!=(const QPointer<T> &p, T *o) |
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249 |
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250 Inequality operator. Returns true if \a o and the guarded |
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251 pointer \a p are not pointing to the same object, otherwise |
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252 returns false. |
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253 */ |
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254 /*! |
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255 \fn bool operator!=(const QPointer<T> &p1, const QPointer<T> &p2) |
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256 |
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257 Inequality operator. Returns true if the guarded pointers \a p1 and |
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258 \a p2 are not pointing to the same object, otherwise |
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259 returns false. |
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260 */ |