C++ - class issue

Question

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:

alt text

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

Thanks.

codaddict · Answer 1 · 2011-01-22T14:24:20.293

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;
                                                         ^^^^^^

score 1 · Answer 2 · answered Jan 22 '11 at 14:18

1

Add

#include <string.h>

And change wage to m_wage on line 19.

answered Jan 22 '11 at 14:18

kynnysmatto

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Please don’t mix C++ and C headers. – Konrad Rudolph Jan 22 '11 at 14:51

score 1 · Answer 3 · answered Jan 22 '11 at 14:20

1

You need :

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

answered Jan 22 '11 at 14:20

nacho4d

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2

Please don’t mix C++ and C headers. – Konrad Rudolph Jan 22 '11 at 14:52

score 1 · Answer 4 · answered Jan 22 '11 at 14:21

1

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.

answered Jan 22 '11 at 14:21

Nikolai Fetissov

82,306
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Santiago Alessandri · Answer 5 · 2011-01-22T16:16:59.803

1

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.

edited Jan 22 '11 at 16:16

answered Jan 22 '11 at 14:22

Santiago Alessandri

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"Please don’t mix C++ and C headers." – Konrad Rudolph :) – Andriy Tylychko Jan 22 '11 at 15:54
thanks for your reply. When you say:"Arrays in C are used through pointers", how then are arrays used in C+=? Thanks. – Simplicity Jan 22 '11 at 20:21
@SWEngineer It applies the same to c++, i wanted to emphasize the difference with other languages. – Santiago Alessandri Jan 22 '11 at 21:46

score 1 · Accepted Answer · answered Jan 22 '11 at 14:24

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.

answered Jan 22 '11 at 14:24

Sdaz MacSkibbons

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Thanks for your reply. You are right, but, why this warning? And, why did we have to insert "const" to gt rid of it? Thanks. – Simplicity Jan 22 '11 at 20:16
With `abder.setInfo("Abder-Rahman",123,400);`, you're passing in a constant string, but you declared `void setInfo(char *strName,int id,double wage)` as `char *`, which indicates to the compiler that you may wish to modify `strName`. The compiler can see that you can't do that, so it is trying to be helpful. Listen to warnings; they almost always help you write more robust code. – Sdaz MacSkibbons Jan 23 '11 at 01:23

C++ - class issue

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