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PO"No known conversion" from const when passing "this" as a parameter
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copied!<p>I am currently making a game which utilizes a state stack manager which keeps track of all the different game states, like the main menu.</p> <p>However, I have encountered a problem which I can't seem to solve.</p> <p>This is the state class, stripped down to only contain the offending code:</p> <pre class="lang-c prettyprint-override"><code>class StateManager; namespace first { namespace second { class State { friend class StateManager; protected: /** * Associates the state with the specified state manager instance. * @param stateManager The instance to associate this state with */ void associateWithManager(StateManager *stateManager) { mStateManager = stateManager; } private: StateManager *mStateManager; }; } // second } // first </code></pre> <p>The following is the state manager, also stripped down:</p> <pre class="lang-c prettyprint-override"><code>namespace first { namespace second { class StateManager { public: /** * Adds a state to the stack. * @param state The state to add */ State &add(State &state) { state.associateWithManager(this); return state; } }; } // second } // first </code></pre> <p>When I try to compile this, I get the following error (line numbers are a bit off, since I have include guards, etc.):</p> <pre><code>src/StateManager.cc: In member function 'State& StateManager::add(State&)': src/StateManager.cc:7:34: error: no matching function for call to 'State::associateWithManager(StateManager* const)' src/StateManager.cc:7:34: note: candidate is: In file included from ./include/StateManager.h:4:0, from src/StateManager.cc:1: ./include/State.h:29:10: note: void State::associateWithManager(StateManager*) ./include/State.h:29:10: note: no known conversion for argument 1 from 'StateManager* const' to 'StateManager*' </code></pre> <p>Apparently, the <code>this</code> pointer is treated like a const pointer, even though I don't use the <code>const</code> keyword on the <code>add</code> method. I'm not sure exactly what is going on here. Is the <code>this</code> pointer always <code>const</code>? I'm pretty sure I've used it this way in the past with no problems though.</p> <p>Also, is the way I'm going about this the 'correct' way? Or is there a better solution when it comes to letting the state know about the manager? Perhaps using a singleton, but I'm not really a big fan of that.</p> <p><strong>EDIT:</strong> I now realize that the forward declaration outside the namespaces was the reason for this. Should I accept Mike's answer, since it helped me come to this conclusion? Or should I post my own?</p>

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