生成文件:体系结构x86_64的未定义符号

我正在使我的应用程序更具可移植性，可以在其他操作系统上运行。在XCode和Visual Studio中工作。但是，切换到Makefiles给我带来了一些问题。

错误：

Undefined symbols for architecture x86_64:                                     
"AppObject::Instance()", referenced from:                        
_main in main-329f6c.o                                                                                          
ld: symbol(s) not found for architecture x86_64

主.cpp

#include <iostream>
#include "AppObject.hpp"
AppObject* _appObject;
int main()
{
_appObject = AppObject::Instance();
return 0;
}

AppObject.hpp

#ifndef  _APPOBJECT_HPP_
#define  _APPOBJECT_HPP_
#include <iostream>
class AppObject
{
public:
static AppObject* Instance();
virtual ~AppObject() {}
void initInstance();
private:
AppObject();
AppObject(const AppObject&);
AppObject& operator= (const AppObject&);
static AppObject* pinstance; 
};
#endif // _APPOBJECT_HPP_

应用对象.cpp

#include "AppObject.hpp"
AppObject* AppObject::pinstance = 0;
AppObject::AppObject() {}
AppObject* AppObject::Instance()
{
if (pinstance == 0)
{
pinstance = new AppObject;
pinstance->initInstance();
}
return pinstance;
}
void AppObject::initInstance()
{
.....
}

这有点配对，但我也看到了其他一些警告：

warning: in-class initialization of non-static data member is a C++11 extension

谁能帮助我理解我的错误，我的这在 XCode 和 VS 中有效，但不使用 make？

生成文件

CXX=clang++
CXXFLAGS=-g -std=c++11 -Wall -pedantic -c
LDFLAGS=-L/usr/local/opt/sqlite/lib
CPPFLAGS=-I/usr/local/opt/sqlite/include
SOURCES=scraper/main.cpp scraper/AppObject.cpp scraper/SQLManager.cpp
OBJECTS=$(SOURCES:.cpp=.o)
EXECUTABLE=scraper
all: $(SOURCES) $(EXECUTABLE)
$(EXECUTABLE): $(OBJECTS) 
$(CXX) $(LDFLAGS) $(OBJECTS) -o $@
.cpp.o:
$(CXX) $(CXXFLAGS) $< -o $@

全制作输出：

$ make
clang  scraper/main.cpp -o scraper/main.o
In file included from scraper/main.cpp:3:
In file included from scraper/AppObject.hpp:6:
scraper/SQLManager.hpp:44:30: warning: in-class initialization of non-    static data member is a C++11 extension
[-Wc++11-extensions]
bool _bDatabaseReady = false;
^
scraper/SQLManager.hpp:46:29: warning: in-class initialization of non-    static data member is a C++11 extension
[-Wc++11-extensions]
std::string _dbFile = "popcorn.db3";
^
scraper/SQLManager.hpp:47:29: warning: in-class initialization of non-    static data member is a C++11 extension
[-Wc++11-extensions]
std::string _dbName = "popcorn";
^
scraper/SQLManager.hpp:49:24: warning: in-class initialization of non-    static data member is a C++11 extension
[-Wc++11-extensions]
int _dbVersion = 1; // increment this when database structure changes
^
scraper/SQLManager.hpp:51:28: warning: in-class initialization of non-static data member is a C++11 extension
[-Wc++11-extensions]
int _dbVersionType = 0; // 0 = normal, 1 = free, 2 = lite
^
5 warnings generated.
Undefined symbols for architecture x86_64:
"AppObject::Instance()", referenced from:
_main in main-4a5276.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see     invocation)
make: *** [scraper/main.o] Error 1

从回复中获取建议后更新make输出：

$ make
clang++  scraper/main.cpp -o scraper/main.o
In file included from scraper/main.cpp:3:
In file included from scraper/AppObject.hpp:6:
scraper/SQLManager.hpp:44:30: warning: in-class initialization of non-    static data member is a C++11 extension [-Wc++11-extensions]
bool _bDatabaseReady = false;
^
scraper/SQLManager.hpp:46:29: warning: in-class initialization of non-    static data member is a C++11 extension [-Wc++11-extensions]
std::string _dbFile = "popcorn.db3";
^
scraper/SQLManager.hpp:47:29: warning: in-class initialization of non-    static data member is a C++11 extension [-Wc++11-extensions]
std::string _dbName = "popcorn";
^
scraper/SQLManager.hpp:49:24: warning: in-class initialization of non-    static data member is a C++11 extension [-Wc++11-extensions]
int _dbVersion = 1; // increment this when database structure changes
^
scraper/SQLManager.hpp:51:28: warning: in-class initialization of non-    static data member is a C++11 extension [-Wc++11-extensions]
int _dbVersionType = 0; // 0 = normal, 1 = free, 2 = lite
^
5 warnings generated.
Undefined symbols for architecture x86_64:
"AppObject::Instance()", referenced from:
_main in main-0e97bb.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see     invocation)
make: *** [scraper/main.o] Error 1