1 | /* |
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2 | * ORXONOX - the hottest 3D action shooter ever to exist |
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3 | * > www.orxonox.net < |
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4 | * |
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5 | * |
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6 | * License notice: |
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7 | * |
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8 | * This program is free software; you can redistribute it and/or |
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9 | * modify it under the terms of the GNU General Public License |
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10 | * as published by the Free Software Foundation; either version 2 |
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11 | * of the License, or (at your option) any later version. |
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12 | * |
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13 | * This program is distributed in the hope that it will be useful, |
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14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
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15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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16 | * GNU General Public License for more details. |
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17 | * |
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18 | * You should have received a copy of the GNU General Public License |
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19 | * along with this program; if not, write to the Free Software |
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20 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. |
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21 | * |
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22 | * Author: |
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23 | * Benjamin Grauer |
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24 | * Fabian 'x3n' Landau |
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25 | * Reto Grieder (direct conversion tests) |
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26 | * Co-authors: |
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27 | * ... |
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28 | */ |
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29 | |
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30 | /*! |
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31 | @file |
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32 | @brief Definition and Implementation of the Convert class. |
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33 | */ |
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34 | |
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35 | #ifndef _Converter_H__ |
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36 | #define _Converter_H__ |
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37 | |
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38 | #include "UtilPrereqs.h" |
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39 | |
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40 | #include <string> |
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41 | #include <sstream> |
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42 | #include <istream> |
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43 | #include <ostream> |
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44 | |
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45 | #include "Debug.h" |
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46 | |
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47 | // Gcc generates warnings when implicitely casting from float to int for instance. |
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48 | // This is however exactly what convertValue does, so we need to suppress the warnings. |
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49 | // They only occur in when using the ImplicitConversion template. |
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50 | #if ORXONOX_COMPILER == ORXONOX_COMPILER_GNUC |
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51 | # pragma GCC system_header |
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52 | #endif |
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53 | |
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54 | /////////////////////////////////////////////// |
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55 | // Static detection for conversion functions // |
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56 | /////////////////////////////////////////////// |
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57 | /* The idea to use the sizeof() operator on return functions to determine function existance |
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58 | is described in 'Moder C++ design' by Alexandrescu (2001). */ |
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59 | |
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60 | // disable warnings about possible loss of data |
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61 | #if ORXONOX_COMPILER == ORXONOX_COMPILER_MSVC |
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62 | # pragma warning(push) |
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63 | # pragma warning(disable:4244) |
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64 | #endif |
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65 | |
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66 | namespace conversionTests |
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67 | { |
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68 | // A struct that is guaranteed to be larger than any return type of our conversion functions. |
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69 | // So we simply add all the sizes of the return types plus a little bit more. |
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70 | struct VeryBigStruct |
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71 | { |
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72 | char intSize[sizeof(int)]; |
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73 | char addingMore[4096]; // just to be sure ;) |
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74 | }; |
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75 | |
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76 | template <class FromType, class ToType> |
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77 | class ImplicitConversion |
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78 | { |
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79 | private: |
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80 | ImplicitConversion(); ImplicitConversion(const ImplicitConversion&); ~ImplicitConversion(); |
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81 | // Gets chosen only if there is an implicit conversion from FromType to ToType. |
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82 | static int test(ToType); |
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83 | // Accepts any argument. Why do we not use a template? The reason is that with templates, |
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84 | // the function above is only taken iff it is an exact type match. But since we want to |
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85 | // check for implicit conversion, we have to use the ellipsis. |
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86 | static VeryBigStruct test(...); |
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87 | static FromType object; // helper object to handle private c'tor and d'tor |
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88 | public: |
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89 | // test(object) only has 'VerySmallStruct' return type iff the compiler doesn't choose test(...) |
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90 | enum { exists = !(sizeof(test(object)) == sizeof(VeryBigStruct)) }; |
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91 | }; |
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92 | } |
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93 | |
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94 | #if ORXONOX_COMPILER == ORXONOX_COMPILER_MSVC |
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95 | # pragma warning(pop) |
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96 | #endif |
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97 | |
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98 | |
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99 | //////////////////////////////////// |
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100 | //// ACTUAL CONVERSION SEQUENCE //// |
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101 | //////////////////////////////////// |
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102 | /* |
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103 | There is a distinct priority when choosing the right conversion function: |
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104 | Overwrites: |
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105 | 1. (Partial) template specialisation of ConverterExplicit::convert |
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106 | 2. Global functions convertValue(ToType* output, const FromType input) |
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107 | Fallbacks: |
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108 | 3. Any possible implicit conversion. This includes FooBar --> int if FooBar defines operator float(). |
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109 | 4. Global or member operators for stringstream when converting from or to std::string (or FROM const char*) |
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110 | 5. Function that simply displays "Could not convert value" with information obtained from typeid(). |
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111 | |
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112 | A note: There has to be an exact type match (or according to the rules of template spec.) except for 3. |
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113 | |
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114 | There are obviously a lot of ways to specifiy a user defined conversion. What should I use? |
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115 | When using any non-template function based conversion (implicit conversion, convertValue, << or >>) |
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116 | then you should consider that this function has to be defined prior to including this file. |
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117 | If you do not whish do do that, you will have to spcecialsize the ConverterExplicit template. |
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118 | There is a not so obvious advantage of the other way (non-template): You could declare each conversion function |
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119 | in the Prereqs file of the corresponding library. Then you can use the conversion everywhere. |
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120 | This is not possible with template specialisations even when defining them in this file (You would create |
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121 | a circular dependency when using a class from Core for instance, because complete template specialisations |
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122 | get compiled anyway (there is no template parameter)). |
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123 | */ |
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124 | |
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125 | namespace |
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126 | { |
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127 | // little template that maps to ints to entire types (Alexandrescu 2001) |
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128 | template <int I> |
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129 | struct Int2Type { }; |
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130 | } |
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131 | |
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132 | |
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133 | /////////////////// |
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134 | // No Conversion // |
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135 | /////////////////// |
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136 | |
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137 | // Default template for fallbackConvert, no conversion possible |
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138 | template <class ToType, class FromType> |
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139 | inline bool fallbackConversion(ToType* output, FromType input) |
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140 | { |
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141 | COUT(2) << "Could not convert value of type " << typeid(FromType).name() |
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142 | << " to type " << typeid(ToType).name() << std::endl; |
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143 | return false; |
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144 | } |
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145 | |
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146 | |
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147 | ///////////////////// |
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148 | // fallbackConvert // |
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149 | ///////////////////// |
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150 | |
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151 | // Class template used when << or >> was not available with string conversions |
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152 | // It is required to call not yet declared fallbackConvert functions. |
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153 | template <class ToType, class FromType> |
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154 | struct ConverterFallbackTemplate |
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155 | { |
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156 | static bool convert(ToType* output, const FromType& input) |
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157 | { |
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158 | return fallbackConversion(output, input); |
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159 | } |
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160 | }; |
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161 | |
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162 | // Default template for stringstream |
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163 | template <class ToType, class FromType> |
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164 | struct ConverterStringStream |
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165 | { |
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166 | static bool convert(ToType* output, const FromType& input) |
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167 | { |
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168 | return fallbackConversion(output, input); |
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169 | } |
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170 | }; |
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171 | |
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172 | |
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173 | ///////////// |
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174 | // OStream // |
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175 | ///////////// |
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176 | |
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177 | namespace fallbackTemplates |
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178 | { |
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179 | template <class FromType> |
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180 | inline bool operator <<(std::ostream& outstream, const FromType& input) |
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181 | { |
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182 | std::string temp; |
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183 | if (ConverterFallbackTemplate<std::string, FromType>::convert(&temp, input)) |
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184 | { |
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185 | std::operator <<(outstream, temp); |
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186 | return true; |
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187 | } |
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188 | else |
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189 | return false; |
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190 | } |
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191 | } |
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192 | |
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193 | // template that evaluates whether OStringStream is possible for conversions to std::string |
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194 | template <class FromType> |
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195 | struct ConverterStringStream<std::string, FromType> |
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196 | { |
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197 | static bool convert(std::string* output, const FromType& input) |
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198 | { |
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199 | using namespace fallbackTemplates; |
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200 | std::ostringstream oss; |
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201 | if (oss << input) |
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202 | { |
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203 | (*output) = oss.str(); |
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204 | return true; |
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205 | } |
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206 | else |
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207 | return false; |
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208 | } |
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209 | }; |
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210 | |
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211 | |
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212 | ///////////// |
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213 | // IStream // |
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214 | ///////////// |
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215 | |
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216 | namespace fallbackTemplates |
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217 | { |
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218 | template <class ToType> |
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219 | inline bool operator >>(std::istream& instream, ToType& output) |
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220 | { |
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221 | return ConverterFallbackTemplate<ToType, std::string> |
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222 | ::convert(&output, static_cast<std::istringstream&>(instream).str()); |
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223 | } |
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224 | } |
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225 | |
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226 | // template that evaluates whether IStringStream is possible for conversions from std::string |
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227 | template <class ToType> |
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228 | struct ConverterStringStream<ToType, std::string> |
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229 | { |
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230 | static bool convert(ToType* output, const std::string& input) |
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231 | { |
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232 | using namespace fallbackTemplates; |
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233 | std::istringstream iss(input); |
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234 | if (iss >> (*output)) |
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235 | { |
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236 | return true; |
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237 | } |
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238 | else |
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239 | return false; |
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240 | } |
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241 | }; |
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242 | |
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243 | |
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244 | /////////////////// |
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245 | // Implicit Cast // |
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246 | /////////////////// |
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247 | |
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248 | // We can cast implicitely |
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249 | template <class ToType, class FromType> |
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250 | inline bool convertImplicitely(ToType* output, const FromType& input, ::Int2Type<true>) |
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251 | { |
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252 | (*output) = static_cast<ToType>(input); |
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253 | return true; |
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254 | } |
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255 | |
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256 | // static cast no possible, try stringstream conversion next |
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257 | template <class ToType, class FromType> |
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258 | inline bool convertImplicitely(ToType* output, const FromType& input, ::Int2Type<false>) |
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259 | { |
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260 | return ConverterStringStream<ToType, FromType>::convert(output, input); |
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261 | } |
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262 | |
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263 | |
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264 | /////////////////////// |
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265 | // Explicit Fallback // |
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266 | /////////////////////// |
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267 | |
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268 | template <class ToType, class FromType> |
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269 | inline bool explicitConversion(ToType* output, const FromType& input) |
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270 | { |
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271 | // try implict conversion by probing first because we use '...' instead of a template |
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272 | const bool probe = conversionTests::ImplicitConversion<FromType, ToType>::exists; |
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273 | return convertImplicitely(output, input, ::Int2Type<probe>()); |
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274 | } |
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275 | |
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276 | |
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277 | // Indirect calls over a class template so we can call functions not yet declared. |
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278 | template <class ToType, class FromType> |
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279 | struct ConverterExplicitTemplate |
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280 | { |
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281 | static bool convert(ToType* output, const FromType& input) |
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282 | { |
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283 | return explicitConversion(output, input); |
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284 | } |
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285 | }; |
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286 | |
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287 | |
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288 | ////////////////////// |
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289 | // Public Functions // |
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290 | ////////////////////// |
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291 | |
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292 | /** |
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293 | @brief |
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294 | Converts any value to any other as long as there exists a conversion. |
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295 | Otherwise, the conversion will generate a runtime warning. |
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296 | For information about the different conversion methods (user defined too), see the section |
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297 | 'Actual conversion sequence' in this file above. |
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298 | @note |
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299 | This function is only a fallback if there is no appropriate 'convertValue' function. |
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300 | */ |
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301 | template <class ToType, class FromType> |
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302 | inline bool convertValue(ToType* output, const FromType& input) |
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303 | { |
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304 | return ConverterExplicitTemplate<ToType, FromType>::convert(output, input); |
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305 | } |
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306 | |
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307 | // For compatibility reasons. The same, but with capital ConvertValue |
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308 | template<class FromType, class ToType> |
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309 | inline bool ConvertValue(ToType* output, const FromType& input) |
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310 | { |
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311 | return convertValue(output, input); |
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312 | } |
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313 | |
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314 | // Calls convertValue and returns true if the conversion was successful. |
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315 | // Otherwise the fallback is used. |
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316 | template<class FromType, class ToType> |
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317 | inline bool ConvertValue(ToType* output, const FromType& input, const ToType& fallback) |
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318 | { |
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319 | if (convertValue(output, input)) |
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320 | return true; |
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321 | |
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322 | (*output) = fallback; |
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323 | return false; |
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324 | } |
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325 | |
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326 | // Directly returns the converted value, even if the conversion was not successful. |
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327 | template<class FromType, class ToType> |
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328 | inline ToType getConvertedValue(const FromType& input) |
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329 | { |
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330 | ToType output; |
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331 | ConvertValue(&output, input); |
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332 | return output; |
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333 | } |
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334 | |
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335 | // Directly returns the converted value, but uses the fallback on failure. |
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336 | template<class FromType, class ToType> |
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337 | inline ToType getConvertedValue(const FromType& input, const ToType& fallback) |
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338 | { |
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339 | ToType output; |
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340 | ConvertValue(&output, input, fallback); |
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341 | return output; |
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342 | } |
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343 | |
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344 | // Like getConvertedValue, but the template argument order is in reverse. |
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345 | // That means you can call it exactly like static_cast<ToType>(fromTypeValue). |
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346 | template<class ToType, class FromType> |
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347 | inline ToType conversion_cast(const FromType& input) |
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348 | { |
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349 | ToType output; |
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350 | ConvertValue(&output, input); |
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351 | return output; |
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352 | } |
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353 | |
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354 | // Like conversion_cast above, but uses a fallback on failure. |
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355 | template<class ToType, class FromType> |
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356 | inline ToType conversion_cast(const FromType& input, const ToType& fallback) |
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357 | { |
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358 | ToType output; |
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359 | ConvertValue(&output, input, fallback); |
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360 | return output; |
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361 | } |
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362 | |
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363 | |
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364 | //////////////////////////////// |
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365 | // Special string conversions // |
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366 | //////////////////////////////// |
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367 | |
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368 | // delegate conversion from const char* to std::string |
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369 | template <class ToType> |
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370 | inline bool explicitConversion(ToType* output, const char* input) |
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371 | { |
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372 | return convertValue<ToType, std::string>(output, input); |
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373 | } |
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374 | |
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375 | // These conversions would exhibit ambiguous << or >> operators when using stringstream |
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376 | inline bool explicitConversion(std::string* output, const char input) |
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377 | { |
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378 | *output = std::string(1, input); |
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379 | return true; |
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380 | } |
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381 | inline bool explicitConversion(std::string* output, const unsigned char input) |
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382 | { |
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383 | *output = std::string(1, input); |
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384 | return true; |
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385 | } |
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386 | inline bool explicitConversion(char* output, const std::string input) |
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387 | { |
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388 | if (input != "") |
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389 | *output = input[0]; |
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390 | else |
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391 | *output = '\0'; |
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392 | return true; |
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393 | } |
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394 | inline bool explicitConversion(unsigned char* output, const std::string input) |
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395 | { |
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396 | if (input != "") |
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397 | *output = input[0]; |
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398 | else |
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399 | *output = '\0'; |
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400 | return true; |
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401 | } |
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402 | |
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403 | #endif /* _Convert_H__ */ |
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