MSVC++ compiler error C2143

问题:

The following code excerpt is responsible for a cryptic MSVC++ compiler error:

template<class T> class Vec : public vector<T>{
  public:
    Vec() : vector<T>(){}
    Vec(int s) : vector<T>(s){}

    T& operator[](int i){return at(i);  }
    const T& operator[](int i)const{ return at(i);}
};

...

The error:

test.cpp(5) : error C2143: syntax error : missing ',' before '<'
  test.cpp(12) : see reference to class template instantiation 'Vec<T>' being compiled

How do I fix this?

---Edit---

Some context:

I am trying to compile code essentially copy and pasted from The C++ Programming Language. I don't yet even understand this code completely. The purpose, however, is to implement a vector type that will throw an exception when some code attempts to access an item out of the vector's range instead of just returning incorrect values.

回答1:

Try

template<class T> class Vec : public vector<T>{
  public:
    Vec() : vector(){} // no <T>
    Vec(int s) : vector(s){} // same

    T& operator[](int i){return at(i);  }
    const T& operator[](int i)const{ return at(i);}
};

The constructor for a template class does not include the template signature in its name.

As a side note, your second constructor should really be

Vec(typename vector<T>::size_type s) : vector(s){} // not necessarily int

Finally, you really shouldn't derive from vector, as it has a non-virtual destructor. Do not attempt to delete a Vec through a pointer to a vector.

回答2:

Why are you attempting to inherit from vector? This will cause you a lot of problems. The least of which is that vector does not have a virtual destructor. This will cause the wrong destructor to be called when deleting a polymorphic reference to your class which will lead to memory leaks or general bad behavior.

For instance, the following code will not call ~Vec() but will call ~vector() instead.

vector<int> *pVec = new Vec<int>();
delete pVec;  // Calls ~vector<T>();

The actual compile error you are seeing though is because you're using the template syntax for the base constructor call. Simply remove that and it should compile

Vec() : vector() {}

回答3:

From MSDN: Compiler Error C2143 (C++)

An unqualified call is made to a type in the Standard C++ Library:

// C2143g.cpp
// compile with: /EHsc /c
#include <vector>
static vector<char> bad;   // C2143
static std::vector<char> good;   // OK

This just bit me. You just have to fix your references to vector<T>, replacing them with std::vector<T>.