C++：静态成员函数和变量-静态变量的重新定义？
我试图将单例设计模式合并到我的代码中，但我开始遇到一个奇怪的错误：
main.obj : error LNK2005: "private: static class gameState * gameState::state" (?state@gameState@@0PAV1@A) already defined in gameState.obj
如果您不熟悉单例模式，它基本上用于在整个程序中仅强制执行某个对象的 1 个实例。 这是相关代码： gameState.h：
class gameState
{
public:
static gameState* Instance() {return state;}
.
.
.
private:
gameState();
static gameState* state;
};
gameState* gameState::state = new gameState();
现在我只是在 main.cpp 文件中使用该对象的实例：
gameState *currState = gameState::Instance();
.
.
.
for_each(currState->getHumanPieces().begin(),currState->getHumanPieces().end(), drawPieces);
似乎我正在尝试重新定义 gameState::state，但无法弄清楚为什么......可以帮助任何人吗？
这解决了这个问题，但仍然存在一个错误，我之前实际上没有发布该错误，因为我认为它只是另一个错误的一部分：
error LNK2019: unresolved external symbol "private: __thiscall gameState::gameState(void)" (??0gameState@@AAE@XZ) referenced in function "void __cdecl `dynamic initializer for 'private: static class gameState * gameState::state''(void)" (??__E?state@gameState@@0PAV1@A@@YAXXZ)
关于如何修复该错误有什么好的建议吗？
谢谢你们两位，已经解决了：D
I was trying to incorporate the Singleton design pattern into my code, but I started getting a weird error:
main.obj : error LNK2005: "private: static class gameState * gameState::state" (?state@gameState@@0PAV1@A) already defined in gameState.obj
If you're not familiar with the singleton pattern, it is basically used to enforce only 1 instance of a certain object in the entire program.
Here is the relevant code:
gameState.h:
class gameState
{
public:
static gameState* Instance() {return state;}
.
.
.
private:
gameState();
static gameState* state;
};
gameState* gameState::state = new gameState();
and right now I'm just using the instance of that object in the main.cpp file:
gameState *currState = gameState::Instance();
.
.
.
for_each(currState->getHumanPieces().begin(),currState->getHumanPieces().end(), drawPieces);
It would seem I am trying to redefine gameState::state, but can't figure out why... help anyone?
that solved that, but one error still remains, which I didn't actually post before as I thought it was just part of the other one:
error LNK2019: unresolved external symbol "private: __thiscall gameState::gameState(void)" (??0gameState@@AAE@XZ) referenced in function "void __cdecl `dynamic initializer for 'private: static class gameState * gameState::state''(void)" (??__E?state@gameState@@0PAV1@A@@YAXXZ)
any good tip on how to fix that one as well?
Thanks both of you, its fixed :D
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评论（3）
您需要将静态
gameState*的定义恰好放入一个源文件中，即这一行：如果将其放入由多个源文件包含的标头中，则每个源文件都有一个
gameState::state这会导致链接时错误。对于后续问题，请使用Vadakkumpadaths建议：您需要为
gameState的构造函数提供定义，而不仅仅是声明。You need to put the definition of the static
gameState*into exactly one source file, i.e. this line:If you put it in a header which is included by multiple source files, each has a definition of
gameState::statewhich leads to errors at link-time.For the follow-up problem, use Vadakkumpadaths advice: you need to provide a definition for
gameStates constructor, not only a declaration.添加构造函数的定义以修复第二个链接器错误。
Add definition for your constructor to fix second linker error.
使用头保护宏来解决重新定义问题，并显式定义您的私有构造函数。
Use a header guard macro for the redefinition problem, and explicitly define your private constructor.