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POerror LNK2001 and error LNK2019 (C++) -- Requesting some learning about these errors
 

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    <p>Alright, so I just finished my last compiler error (so I thought) and these errors came up:</p> <pre><code>1&gt;GameEngine.obj : error LNK2001: unresolved external symbol "public: static double WeaponsDB::PI" (?PI@WeaponsDB@@2NA) 1&gt;Component.obj : error LNK2001: unresolved external symbol "public: static double WeaponsDB::PI" (?PI@WeaponsDB@@2NA) 1&gt;Coordinate.obj : error LNK2019: unresolved external symbol "public: static double WeaponsDB::PI" (?PI@WeaponsDB@@2NA) referenced in function "public: double __thiscall Coordinate::distanceFrom(class Coordinate *)" (?distanceFrom@Coordinate@@QAENPAV1@@Z) 1&gt;Driver.obj : error LNK2001: unresolved external symbol "public: static double WeaponsDB::PI" (?PI@WeaponsDB@@2NA) 1&gt;Environment.obj : error LNK2001: unresolved external symbol "public: static double WeaponsDB::PI" (?PI@WeaponsDB@@2NA) 1&gt;Environment.obj : error LNK2001: unresolved external symbol "public: static bool Environment::spyFlag" (?spyFlag@Environment@@2_NA) 1&gt;Environment.obj : error LNK2001: unresolved external symbol "private: static class Environment * Environment::instance_" (?instance_@Environment@@0PAV1@A) 1&gt;Environment.obj : error LNK2019: unresolved external symbol "public: static void __cdecl Environment::spyAlertOver(void)" (?spyAlertOver@Environment@@SAXXZ) referenced in function "public: void __thiscall Environment::notificationOfSpySuccess(void)" (?notificationOfSpySuccess@Environment@@QAEXXZ) 1&gt;GameDriver.obj : error LNK2019: unresolved external symbol "public: static void __cdecl MainMenu::gameOver(int)" (?gameOver@MainMenu@@SAXH@Z) referenced in function "public: static void __cdecl GameDriver::run(void)" (?run@GameDriver@@SAXXZ) 1&gt;GameDriver.obj : error LNK2019: unresolved external symbol "public: static void __cdecl GameDriver::gatherInput(void)" (?gatherInput@GameDriver@@SAXXZ) referenced in function "public: static void __cdecl GameDriver::run(void)" (?run@GameDriver@@SAXXZ) 1&gt;GameDriver.obj : error LNK2019: unresolved external symbol "public: static void __cdecl GameDriver::ticker(void)" (?ticker@GameDriver@@SAXXZ) referenced in function "public: static void __cdecl GameDriver::run(void)" (?run@GameDriver@@SAXXZ) 1&gt;GameDriver.obj : error LNK2001: unresolved external symbol "public: static int GameDriver::ticks" (?ticks@GameDriver@@2HA) 1&gt;GameDriver.obj : error LNK2001: unresolved external symbol "public: static bool GameDriver::evaluatingInputFlag" (?evaluatingInputFlag@GameDriver@@2_NA) 1&gt;GameDriver.obj : error LNK2001: unresolved external symbol "public: static bool GameDriver::keyQuitFlag" (?keyQuitFlag@GameDriver@@2_NA) 1&gt;GameDriver.obj : error LNK2001: unresolved external symbol "public: static bool GameDriver::keyToggleWeaponRightFlag" (?keyToggleWeaponRightFlag@GameDriver@@2_NA) 1&gt;GameDriver.obj : error LNK2001: unresolved external symbol "public: static bool GameDriver::keyToggleWeaponLeftFlag" (?keyToggleWeaponLeftFlag@GameDriver@@2_NA) 1&gt;GameDriver.obj : error LNK2001: unresolved external symbol "public: static bool GameDriver::keyFireFlag" (?keyFireFlag@GameDriver@@2_NA) 1&gt;GameDriver.obj : error LNK2001: unresolved external symbol "public: static bool GameDriver::keyLeftFlag" (?keyLeftFlag@GameDriver@@2_NA) 1&gt;GameDriver.obj : error LNK2001: unresolved external symbol "public: static bool GameDriver::keyRightFlag" (?keyRightFlag@GameDriver@@2_NA) 1&gt;GameDriver.obj : error LNK2001: unresolved external symbol "public: static bool GameDriver::keyUpFlag" (?keyUpFlag@GameDriver@@2_NA) 1&gt;GameDriver.obj : error LNK2001: unresolved external symbol "public: static bool GameDriver::keyDownFlag" (?keyDownFlag@GameDriver@@2_NA) 1&gt;GUI_Env.obj : error LNK2001: unresolved external symbol "private: static struct BITMAP * GUI_Env::buffer" (?buffer@GUI_Env@@0PAUBITMAP@@A) 1&gt;GUI_Info.obj : error LNK2001: unresolved external symbol "private: static struct BITMAP * GUI_Info::buffer" (?buffer@GUI_Info@@0PAUBITMAP@@A) 1&gt;MenuDriver.obj : error LNK2019: unresolved external symbol "public: static void __cdecl MainMenu::displayMenu(void)" (?displayMenu@MainMenu@@SAXXZ) referenced in function "public: static void __cdecl MenuDriver::start(void)" (?start@MenuDriver@@SAXXZ) 1&gt;SpaceObjectFactory.obj : error LNK2001: unresolved external symbol "private: static class SpaceObjectFactory * SpaceObjectFactory::_instance" (?_instance@SpaceObjectFactory@@0PAV1@A) 1&gt;Spy.obj : error LNK2019: unresolved external symbol "public: virtual bool __thiscall UnFormationable::sameTypeOfSpaceObjectAs(class SpaceObject *)" (?sameTypeOfSpaceObjectAs@UnFormationable@@UAE_NPAVSpaceObject@@@Z) referenced in function "public: virtual bool __thiscall Spy::sameTypeOfSpaceObjectAs(class SpaceObject *)" (?sameTypeOfSpaceObjectAs@Spy@@UAE_NPAVSpaceObject@@@Z) 1&gt;WeaponsDB.obj : error LNK2001: unresolved external symbol "private: static class WeaponsDB * WeaponsDB::_instance" (?_instance@WeaponsDB@@0PAV1@A) 1&gt;C:\Users\Owner\Desktop\Bosconian\code\Bosconian\Debug\Bosconian.exe : fatal error LNK1120: 23 unresolved externals </code></pre> <p>Alright, here's a brief overview.</p> <p>PI is a static constant in WeaponsDB and is referenced by other classes using WeaponsDB::PI and the appropriate #include (what's wrong with this?)</p> <p>Most other errors stem from static variables and static methods for timers from the allegro gaming library.</p> <p>What causes these errors and how might I get rid of them?</p> <p>Thanks in advance</p> <p>----------------Edits-------------------</p> <p>As requested, where the WeaponsDB::PI is declared and defined. It is declared in WeaponsDB.h:</p> <pre><code>public: static double PI; </code></pre> <p>But it is defined in another class Driver.cpp:</p> <pre><code>WeaponsDB::PI = 4*atan(1.0); </code></pre> <p>If this is one of the problems with my code I would love to know why this causes an error.</p>
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    1. COYou need to post the part of the .h file that declares the PI and in the .cpp file that defines it.
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