C++ error constructor parameter

问题

i'm playing around with inheritance. I'm completely baffled by the compiler error i'm getting and looking it up it seems completely unrelated to what i'm trying to do which is simply initialize my class.

here are the errors:

    In file included from main.cpp:2:0:
student.h: In constructor ‘Student::Student(std::string, int, std::string, double)’:
student.h:13:3: error: class ‘Student’ does not have any field named ‘gnu_dev_major’
student.h: In function ‘std::ostream& operator<<(std::ostream&, const Student&)’:
student.h:25:8: error: no match for ‘operator<<’ in ‘os << "Name\011: "’
student.h:25:8: note: candidates are:
student.h:24:16: note: std::ostream& operator<<(std::ostream&, const Student&)
student.h:24:16: note:   no known conversion for argument 2 from ‘const char [8]’ to ‘const Student&’
/usr/include/c++/4.6/bits/basic_string.h:2693:5: note: template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
student.h:25:32: error: ‘endl’ is not a member of ‘std’
student.h:26:8: error: no match for ‘operator<<’ in ‘os << "Age\011: "’
student.h:26:8: note: candidates are:
student.h:24:16: note: std::ostream& operator<<(std::ostream&, const Student&)
student.h:24:16: note:   no known conversion for argument 2 from ‘const char [7]’ to ‘const Student&’
/usr/include/c++/4.6/bits/basic_string.h:2693:5: note: template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
student.h:26:30: error: ‘endl’ is not a member of ‘std’
student.h:27:8: error: no match for ‘operator<<’ in ‘os << "Major\011: "’
student.h:27:8: note: candidates are:
student.h:24:16: note: std::ostream& operator<<(std::ostream&, const Student&)
student.h:24:16: note:   no known conversion for argument 2 from ‘const char [9]’ to ‘const Student&’
/usr/include/c++/4.6/bits/basic_string.h:2693:5: note: template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
student.h:27:34: error: ‘endl’ is not a member of ‘std’
student.h:28:8: error: no match for ‘operator<<’ in ‘os << "GPA\011: "’
student.h:28:8: note: candidates are:
student.h:24:16: note: std::ostream& operator<<(std::ostream&, const Student&)
student.h:24:16: note:   no known conversion for argument 2 from ‘const char [7]’ to ‘const Student&’
/usr/include/c++/4.6/bits/basic_string.h:2693:5: note: template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
student.h:28:30: error: ‘endl’ is not a member of ‘std’
main.cpp: In function ‘int main()’:
main.cpp:8:2: error: ‘cout’ was not declared in this scope

whats confusing me is the very first error i'm getting:

student.h: In constructor ‘Student::Student(std::string, int, std::string, double)’: student.h:13:3: error: class ‘Student’ does not have any field named ‘gnu_dev_major’

here is my code:

  1 #ifndef STUDENT_H
  2 #define STUDENT_H
  3 
  4 #include <iostream>
  5 #include <string>
  6 #include "person.h"
  7 
  8 class Student : public Person {
  9         friend std::ostream & operator<<(std::ostream &,const Student &);
 10 public:
 11         Student(std::string name, int age, std::string m="undecided", double gpa=0.0) :
 12                 Person::Person(name,age),
 13                 major(m),
 14                 gpa(gpa)
 15         {}
 16 
 17 
 18 
 19 protected:
 20         double gpa;
 21         std::string major;
 22 };
 23 
 24 std::ostream & operator<<(std::ostream &os,const Student &s){
 25         os << "Name\t: " << s.name << std::endl;
 26         os << "Age\t: " << s.age << std::endl;
 27         os << "Major\t: " << s.major << std::endl;
 28         os << "GPA\t: " << s.gpa << std::endl;
 29 }
 30 
 31 #endif

also if anyone has a pointer as to what might be going wrong in my overloaded operator << help with that is also appreciated =).

回答1:

You need to declare your overloaded << operator as friend inside your class:

Inside your Student class declare it as follows:

class Student {
    // rest of code
    friend std::ostream & operator<<(std::ostream &os,const Student &s);
}

来源：https://stackoverflow.com/questions/20024722/c-error-constructor-parameter

标签

c++

operator-overloading