C++ - class issue

问题:

At: http://www.learncpp.com/cpp-tutorial/82-classes-and-class-members/

There is the following program (I made some small modifications):

#include <iostream>

class Employee
{
public:
    char m_strName[25];
    int m_id;
    double m_wage;

    //set the employee information
    void setInfo(char *strName,int id,double wage)
    {
        strncpy(m_strName,strName,25);
        m_id=id;
        m_wage=wage;
    }

    //print employee information to the screen
    void print()
    {
        std::cout<<"Name: "<<m_strName<<"id: "<<m_id<<"wage: $"<<wage<<std::endl;
    }
};

int main()
{
    //declare employee
    Employee abder;
    abder.setInfo("Abder-Rahman",123,400);
    abder.print();
    return 0;
}

When I try to compile it, I get the following:

And, why is a pointer used here? void setInfo(char *strName,int id,double wage)

Thanks.

回答1:

1.

strncpy(m_strName,strName,25);

You need to #include <cstring> (where strncpy is declared).

2.

std::cout<<"Name: "<<m_strName<<"id: "<<m_id<<"wage: $"<<wage<<std::endl;

should be

std::cout<<"Name: "<<m_strName<<"id: "<<m_id<<"wage: $"<<m_wage<<std::endl;

3.

void setInfo(char *strName,int id,double wage)

can be set to

void setInfo(const char *strName,int id,double wage)

to get rid of the g++ 4.x.x warning.

回答2:

You'll have to include the header that declares the strncpy function. So add

#include <cstring> 

at the beginning.

And the member name is m_wage but you've used it as wage in your print member function.

Change

std::cout<<"Name: "<<m_strName<<"id: "<<m_id<<"wage: $"<<wage<<std::endl;

to

std::cout<<"Name: "<<m_strName<<"id: "<<m_id<<"wage: $"<<m_wage<<std::endl;
                                                         ^^^^^^

回答3:

Add

#include <string.h>

And change wage to m_wage on line 19.

回答4:

You need :

#include <string>
#include <iostream>
#include <string.h>

回答5:

Regarding the last warning/error message - the first parameter of the setInfo() member function should be declared as const char*. Plain char* represents pointer to a mutable character array, which string literal "Abder-Rahman" isn't.

回答6:

The error is because strncpy is declared in the cstring header file.

A pointer is used because you are working with C strings, which are char arrays. Arrays in C are used through pointers. And strncpy takes two pointers to char(char arrays) to do the copy process.