編譯C++時體系結構x86_64的未定義符號

Question

我不斷地收到這個錯誤，這讓我瘋狂！

Undefined symbols for architecture x86_64: 
    "SSResourcesDepot::_sharedInstance", referenced from: 
    SSResourcesDepot::sharedInstance() in SSResourcesDepot.o 
ld: symbol(s) not found for architecture x86_64 
clang: error: linker command failed with exit code 1 (use -v to see invocation) 

我的代碼如下所示：

#ifndef SolarSystem_SSResourcesDepot_h 
#define SolarSystem_SSResourcesDepot_h 
#include "SSResource.h" 

/* SSResourcesDepot is implemented as a Singleton Depot that keeps track of all 
* requested Resource objects, and avoid loading them twice in memory. */ 
class SSResourcesDepot { 

    SSResourcesDepot() {}; 
    SSResourcesDepot(SSResourcesDepot const&){}; 
    SSResourcesDepot& operator=(SSResourcesDepot const&){}; 

    static SSResourcesDepot* _sharedInstance; 

    SSResource* _search(std::string resourceName); 
    SSResource* _load(std::string resourceName); 

public: 
    static SSResourcesDepot* sharedInstance(); 
    SSResource* requestResource(std::string resourceName); 

}; 

#endif 

和：

#include <iostream> 
#include "SSResourcesDepot.h" 


#pragma mark Public methods 
SSResourcesDepot* SSResourcesDepot::sharedInstance() { 
    if (SSResourcesDepot::_sharedInstance == 0) { 
     SSResourcesDepot::_sharedInstance = new SSResourcesDepot(); 
    } 
    return SSResourcesDepot::_sharedInstance; 
} 

SSResource* SSResourcesDepot::requestResource(std::string resourceName) { 
    SSResource *resource = this->_search(resourceName); 
    if (resource == NULL) resource = this->_load(resourceName); 
    return resource; 
} 


#pragma mark Private methods 
SSResource* SSResourcesDepot::_search(std::string resourceName) { 
    return NULL; 
} 

SSResource* SSResourcesDepot::_load(std::string resourceName) { 
    return NULL; 
} 

似乎完全的功能給我，但蘋果-O-匹配器不斷抱怨，它不會讓我編譯...：-S

在此先感謝！

Answer 1

您沒有初始化您的static成員。

添加

SSResourcesDepot* SSResourcesDepot::_sharedInstance = NULL; 

您實現文件。