src/library_loader.h

   1 /*
   2  * This file is part of OpenTTD.
   3  * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
   4  * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   5  * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
   6  */
   7
   8 /** @file library_loader.h Functions/types related to loading libraries dynamically. */
   9
  10 #ifndef LIBRARY_LOADER_H
  11 #define LIBRARY_LOADER_H
  12
  13 class LibraryLoader {
  14 public:
  15         /**
  16          * A function loaded from a library.
  17          *
  18          * Will automatically cast to the correct function pointer type on retrieval.
  19          */
  20         class Function {
  21         public:
  22                 explicit Function(void *p) : p(p) {}
  23
  24                 template <typename T, typename = std::enable_if_t<std::is_function_v<T>>>
  25                 operator T *() const
  26                 {
  27                         return reinterpret_cast<T *>(this->p);
  28                 }
  29
  30         private:
  31                 void *p;
  32         };
  33
  34         /**
  35          * Load a library with the given filename.
  36          */
  37         explicit LibraryLoader(const std::string &filename)
  38         {
  39                 this->handle = this->OpenLibrary(filename);
  40         }
  41
  42         /**
  43          * Close the library.
  44          */
  45         ~LibraryLoader()
  46         {
  47                 if (this->handle != nullptr) {
  48                         this->CloseLibrary();
  49                 }
  50         }
  51
  52         /**
  53          * Check whether an error occurred while loading the library or a function.
  54          *
  55          * @return Whether an error occurred.
  56          */
  57         bool HasError()
  58         {
  59                 return this->error.has_value();
  60         }
  61
  62         /**
  63          * Get the last error that occurred while loading the library or a function.
  64          *
  65          * @return The error message.
  66          */
  67         std::string GetLastError()
  68         {
  69                 return this->error.value_or("No error");
  70         }
  71
  72         /**
  73          * Get a function from a loaded library.
  74          *
  75          * @param symbol_name The name of the function to get.
  76          * @return The function. Check HasError() before using.
  77          */
  78         Function GetFunction(const std::string &symbol_name)
  79         {
  80                 if (this->error.has_value()) return Function(nullptr);
  81                 return Function(this->GetSymbol(symbol_name));
  82         }
  83
  84 private:
  85         /**
  86          * Open the library with the given filename.
  87          *
  88          * Should set error if any error occurred.
  89          *
  90          * @param filename The filename of the library to open.
  91          */
  92         void *OpenLibrary(const std::string &filename);
  93
  94         /**
  95          * Close the library.
  96          */
  97         void CloseLibrary();
  98
  99         /**
 100          * Get a symbol from the library.
 101          *
 102          * Should set error if any error occurred.
 103          *
 104          * @param symbol_name The name of the symbol to get.
 105          */
 106         void *GetSymbol(const std::string &symbol_name);
 107
 108         std::optional<std::string> error = {}; ///< The last error that occurred, if set.
 109         void *handle = nullptr; ///< Handle to the library.
 110 };
 111
 112 #endif /* LIBRARY_LOADER_H */