Question

undefined reference to 错误

写了一个最小程序，代码如下：

class1.h:
#ifndef class1_h
#define class1_h

namespace mainprogram {
class class1
{
public:
class1();
virtual ~class1() { }
};
}

#endif // class1_h

class1.cpp:
# include "class1.h"
namespace mainprogram {
class class1
{

class1 :: class1()
{
cout << "Hello world!" << endl;
}

}
}

main.cpp:
#include <iostream>
#include "class1.h"

using namespace std;
using namespace mainprogram;

int main()
{
cout << "Hello world!" << endl;
class1 c11;
return 0;
}

报错提示：undefined reference to `mainprogram::class1::class1()'

Answer 1

class1.cpp里面

class1.cpp:
# include "class1.h"
namespace mainprogram {
//class class1
//{

class1 :: class1()
{
  cout << "Hello world!" << endl;
}

//}
}