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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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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 #include "qscopedpointer.h" |
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43 |
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44 QT_BEGIN_NAMESPACE |
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45 |
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46 /*! |
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47 \class QScopedPointer |
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48 \brief The QScopedPointer class stores a pointer to a dynamically allocated object, and deletes it upon destruction. |
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49 \since 4.6 |
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50 \reentrant |
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51 \ingroup misc |
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52 |
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53 Managing heap allocated objects manually is hard and error prone, with the |
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54 common result that code leaks memory and is hard to maintain. |
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55 QScopedPointer is a small utility class that heavily simplifies this by |
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56 assigning stack-based memory ownership to heap allocations, more generally |
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57 called resource acquisition is initialization(RAII). |
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58 |
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59 QScopedPointer guarantees that the object pointed to will get deleted when |
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60 the current scope dissapears. |
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61 |
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62 Consider this function which does heap allocations, and have various exit points: |
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63 |
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64 \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 0 |
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65 |
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66 It's encumbered by the manual delete calls. With QScopedPointer, the code |
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67 can be simplified to: |
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68 |
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69 \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 1 |
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70 |
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71 The code the compiler generates for QScopedPointer is the same as when |
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72 writing it manually. Code that makes use of \a delete are candidates for |
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73 QScopedPointer usage (and if not, possibly another type of smart pointer |
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74 such as QSharedPointer). QScopedPointer intentionally has no copy |
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75 constructor or assignment operator, such that ownership and lifetime is |
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76 clearly communicated. |
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77 |
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78 The const qualification on a regular C++ pointer can also be expressed with |
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79 a QScopedPointer: |
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80 |
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81 \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 2 |
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82 |
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83 \section1 Custom cleanup handlers |
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84 |
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85 Arrays as well as pointers that have been allocated with \c malloc must |
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86 not be deleted using \c delete. QScopedPointer's second template parameter |
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87 can be used for custom cleanup handlers. |
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88 |
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89 The following custom cleanup handlers exist: |
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90 |
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91 \list |
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92 \i QScopedPointerDeleter - the default, deletes the pointer using \c delete |
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93 \i QScopedPointerArrayDeleter - deletes the pointer using \c{delete []}. Use |
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94 this handler for pointers that were allocated with \c{new []}. |
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95 \i QScopedPointerPodDeleter - deletes the pointer using \c{free()}. Use this |
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96 handler for pointers that were allocated with \c{malloc()}. |
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97 \endlist |
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98 |
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99 You can pass your own classes as handlers, provided that they have a public |
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100 static function \c{void cleanup(T *pointer)}. |
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101 |
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102 \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 5 |
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103 |
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104 \section1 Forward Declared Pointers |
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105 |
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106 Classes that are forward declared can be used within QScopedPointer, as |
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107 long as the destructor of the forward declared class is available whenever |
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108 a QScopedPointer needs to clean up. |
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109 |
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110 Concretely, this means that all classes containing a QScopedPointer that |
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111 points to a forward declared class must have non-inline constructors, |
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112 destructors and assignment operators: |
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113 |
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114 \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 4 |
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115 |
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116 Otherwise, the compiler output a warning about not being able to destruct |
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117 \c MyPrivateClass. |
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118 |
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119 \sa QSharedPointer |
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120 */ |
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121 |
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122 /*! \typedef QScopedPointer::pointer |
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123 \internal |
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124 */ |
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125 |
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126 /*! |
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127 \fn QScopedPointer::QScopedPointer(T *p = 0) |
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128 |
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129 Constructs this QScopedPointer instance and sets its pointer to \a p. |
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130 */ |
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131 |
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132 /*! |
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133 \fn QScopedPointer::~QScopedPointer() |
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134 |
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135 Destroys this QScopedPointer object. Delete the object its pointer points |
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136 to. |
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137 */ |
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138 |
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139 /*! |
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140 \fn T *QScopedPointer::data() const |
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141 |
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142 Returns the value of the pointer referenced by this object. QScopedPointer |
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143 still owns the object pointed to. |
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144 */ |
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145 |
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146 /*! |
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147 \fn T &QScopedPointer::operator*() const |
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148 |
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149 Provides access to the scoped pointer's object. |
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150 |
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151 If the contained pointer is \c null, behavior is undefined. |
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152 \sa isNull() |
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153 */ |
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154 |
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155 /*! |
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156 \fn T *QScopedPointer::operator->() const |
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157 |
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158 Provides access to the scoped pointer's object. |
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159 |
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160 If the contained pointer is \c null, behavior is undefined. |
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161 |
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162 \sa isNull() |
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163 */ |
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164 |
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165 /*! |
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166 \fn QScopedPointer::operator bool() const |
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167 |
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168 Returns \c true if this object is not \c null. This function is suitable |
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169 for use in \tt if-constructs, like: |
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170 |
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171 \snippet doc/src/snippets/code/src_corelib_tools_qscopedpointer.cpp 3 |
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172 |
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173 \sa isNull() |
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174 */ |
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175 |
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176 /*! |
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177 \fn bool QScopedPointer::operator==(const QScopedPointer<T, Cleanup> &other) const |
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178 |
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179 Equality operator. Returns true if the scoped pointer \a other |
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180 is pointing to the same object as this pointer, otherwise returns false. |
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181 */ |
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182 |
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183 |
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184 /*! |
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185 \fn bool QScopedPointer::operator!=(const QScopedPointer<T, Cleanup> &other) const |
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186 |
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187 Inequality operator. Returns true if the scoped pointer \a other |
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188 is not pointing to the same object as this pointer, otherwise returns false. |
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189 */ |
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190 |
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191 /*! |
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192 \fn bool QScopedPointer::isNull() const |
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193 |
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194 Returns \c true if this object is holding a pointer that is \c null. |
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195 */ |
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196 |
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197 /*! |
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198 \fn void QScopedPointer::reset(T *other = 0) |
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199 |
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200 Deletes the existing object it is pointing to if any, and sets its pointer to |
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201 \a other. QScopedPointer now owns \a other and will delete it in its |
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202 destructor. |
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203 */ |
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204 |
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205 /*! |
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206 \fn T *QScopedPointer::take() |
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207 |
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208 Returns the value of the pointer referenced by this object. The pointer of this |
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209 QScopedPointer object will be reset to \c null. |
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210 |
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211 Callers of this function take ownership of the pointer. |
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212 */ |
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213 |
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214 /*! \fn bool QScopedPointer::operator!() const |
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215 |
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216 Returns \c true if the pointer referenced by this object is \c null, otherwise |
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217 returns \c false. |
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218 |
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219 \sa isNull() |
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220 */ |
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221 |
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222 /*! \fn void QScopedPointer::swap(QScopedPointer<T, Cleanup> &other) |
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223 Swap this pointer with \a other. |
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224 */ |
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225 |
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226 QT_END_NAMESPACE |