错误：上课前应有类型说明符

Question

I am a java dev, learning c++. This following sample code doesn't compile and I couldn't find a clue.

#include <iostream>
#include <cstdlib>
#include <string>
#include <stdexcept>

using namespace std;

template <class T>
class MyObj {

  public:
  T value;
  MyObj(T a){
      this.value = a;
  }
}; 

template <class T>
inline MyObj<T> const& sum(MyObj<T> const& a, MyObj<T> const& b) 
{ 
    // append copy of passed element 
    T result = a.value+b.value;
    MyObj<T> obj = new MyObj(result);

    return obj;
}

int main() 
{ 
    try {
        MyObj<int> s1 = new MyObj(1);
        MyObj<int> s2 = new MyObj(3);

        MyObj<int> s3 = sum(s1,s2);

        cout << s3.value <<endl; 
    } 
    catch (exception const& ex) {
        cerr << "Exception: " << ex.what() <<endl; 
        return -1;
    } 
} 

It returns -

main.cpp:31:29: error: expected type-specifier before 'MyObj' MyObj s1 = new MyObj(1);

and

main.cpp:32:29: error: expected type-specifier before 'MyObj' MyObj s2 = new MyObj(3);

Any help would be appreciated.

Answer 1

With new you are allocating memory on the heap, and so you need a pointer to point to that newly allocated memory: MyObj<int>* s1 = new MyObj(1);

Next, MyObj is a template class, so you have to specify T when you call the construtor: MyObj<int>* s1 = new MyObj<int>(1);

Because s1 and s2 are now pointers, sum can't accept them as pointers, you have deference them to get the values: sum(*s1, *s2);

As @rgettman pointed out, this is a pointer, and so must be acessed using -> and not . .