std lib对象作为返回类型和函数参数

Question

I am new to C++ and the idea of header files defining classes is foreign to me. I have the following header file for a Polynomial class that is giving me a lot of errors.

#ifndef POLYNOMIAL_H
#define POLYNOMIAL_H

class Polynomial {
public:
    Polynomial(std::vector <int>&);
    Polynomial(const Polynomial& orig);
    virtual ~Polynomial();

    std::vector <int> getCoeffs();
    Polynomial getIntegral(int, int, int);
    Polynomial getDerivative(int);
    std::string toString();

    void integrate(int, int);
    void derive();
private:
    std::vector<int> coeffs;
};

 #endif /* POLYNOMIAL_H */

All of the class methods that include something from the standard lib in their return type definition give me the error: 'vector' (or 'string') in namespace 'std' does not name a type

Also the constructor which takes a vector as a parameter gives the error: expected ')' before '<' token.

I'm sure this is something very obvious, but whatever it is the tutorials I have done haven't gone this deep into classes and class definitions to come across an example like this.

Answer 1

std::vector is defined in the header vector . You need to add the statement

#include <vector>

at the top of your header file. This causes the preprocessor to (effectively) paste the contents of that file in place of the #include statement. Thus the compiler knows what the type std::vector refers to in your class definition.

The same applies to std::string , which is, in turn, defined in the header string . So add #include <string> for that header.

cppreference.com is a good reference to search for types and their respective headers; it is also a good online reference in general for C++.

This is what your header file should look like:

#ifndef POLYNOMIAL_H
#define POLYNOMIAL_H

#include <string>
#include <vector>

class Polynomial {
  ...
};

#endif /* POLYNOMIAL_H */