Problem with static data members

[toefraz]

Hey, guys. I have an assignment to work with static data members with numbers. I've done all the programming needed, but I keep getting this error when I try to compile:

1>Number.obj : error LNK2005: "private: static class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > * Number::tens" (?tens@Number@@0PAV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@A) already defined in driver.obj
1>Number.obj : error LNK2005: "private: static class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > * Number::lessThan20" (?lessThan20@Number@@0PAV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@A) already defined in driver.obj
1>C:\Users\Tommy\Documents\Visual Studio 2008\Projects\Homework 1_25\Debug\Homework 1_25.exe : fatal error LNK1169: one or more multiply defined symbols found

I've gone through my files one by one and cannot find why these string arrays are being declared twice. It's probably something simple, but I don't see it. Please help, guys. I know you're capable. :-)

Here are my files:

Header file for class:

// Number Class
// 
// Each instance of Number represents a positive 
// integer in the range of 0 to 99. The method inWords()
// should return a string that represents the value.
//
// For example, if the value is 24
// inWords() should return "twenty four"
//
 
#ifndef H_NUMBER
#define H_NUMBER
 
#include <iostream>
#include <string>
 
using namespace std;
 
// Constants for array sizes
const int LT20_SIZE = 21;
const int TENS_SIZE = 9;
 
 
// Declaration of Number class
class Number
{
private:
    int value;    // To hold a number
 
    // Static arrays to hold words
    static string lessThan20[LT20_SIZE];
    static string tens[TENS_SIZE];
 
public:
 
    // Constructor
    Number(int x);
 
    // Function to return the words for the number
    string inWords();
};
 
// Static member variables must be defined
// outside of the class 
string Number::lessThan20[LT20_SIZE] =
{       "zero", "one", "two", "three", "four", "five",
        "six", "seven", "eight", "nine", "ten", 
        "eleven", "twelve", "thirteen", "fourteen", 
        "fifteen", "sixteen", "seventeen", "eighteen",
        "nineteen"
};
 
string Number::tens[TENS_SIZE] = 
{       "twenty", "thirty", "fourty", "fifty",
        "sixty", "seventy", "eighty", "ninety"
};
 
#endif

Class source:

#include "Number.h"
#include <string>
#include <iostream>
 
using namespace std;
 
Number::Number( int x )
{
    if ( (x >= 0) && (x <= 99) )
        Number::value = x;
    else
        exit(EXIT_FAILURE);
}
 
string Number::inWords()
{
    int temp = value;
    string a, b;
 
    if ( temp < 20 )
        return lessThan20[value];
    else
    {
        temp /= 10;
 
        a = tens[temp - 2];
 
        if ( (value - (temp * 10)) == 0 )
            return a;
        else
        {
            b = lessThan20[(value - (temp * 10))];
            return a + ' ' + b;
            }
    }
}

Driver file provided by instructor:

#include "Number.h"
#include <iostream>
#include <string>
 
using namespace std;
 
// Program to test the Number class
int main()
{
    // create a Number instance, passing an integer to the constructor
    Number n(0);
 
    // get the Number's value in words
    string s;
    s = n.inWords();
 
    // print out a message
    cout << "0 is " << s << endl;
 
 
    // try more test cases
    Number o(3);
    cout << "3 is " << o.inWords() << endl;
 
    Number p(13);
    cout << "13 is " << p.inWords() << endl;
 
    Number q(20);
    cout << "20 is " << q.inWords() << endl;
 
    Number r(23);
    cout << "23 is " << r.inWords() << endl;
 
    Number t(47);
    cout << "47 is " << t.inWords() << endl;
 
    return 0;
}

Thanks.

[weaknessforcats]

Try putting your class in the header file number.h and the member function in number.cpp:

Number.h:

#ifndef NUMBERH
#define NUMBERH
// Constants for array sizes
const int LT20_SIZE = 21;
const int TENS_SIZE = 9;
 
 
// Declaration of Number class
class Number
{
private:
    int value;    // To hold a number
 
    // Static arrays to hold words
    static string lessThan20[LT20_SIZE];
    static string tens[TENS_SIZE];
 
public:
 
    // Constructor
    Number(int x);
 
    // Function to return the words for the number
    string inWords();
};
#endif
 

Number.cpp:

#include "number.h"
 /////////////////////////////////////////////////////////////////////////////////
// Static member variables must be defined
// outside of the class 
string Number::lessThan20[LT20_SIZE] =
{       "zero", "one", "two", "three", "four", "five",
        "six", "seven", "eight", "nine", "ten", 
        "eleven", "twelve", "thirteen", "fourteen", 
        "fifteen", "sixteen", "seventeen", "eighteen",
        "nineteen"
};
 
string Number::tens[TENS_SIZE] = 
{       "twenty", "thirty", "fourty", "fifty",
        "sixty", "seventy", "eighty", "ninety"
};
Number::Number( int x )
{
    if ( (x >= 0) && (x <= 99) )
        Number::value = x;
    else
        exit(EXIT_FAILURE);
}
 
string Number::inWords()
{
    int temp = value;
    string a, b;
 
    if ( temp < 20 )
        return lessThan20[value];
    else
    {
        temp /= 10;
 
        a = tens[temp - 2];
 
        if ( (value - (temp * 10)) == 0 )
            return a;
        else
        {
            b = lessThan20[(value - (temp * 10))];
            return a + ' ' + b;
            }
    }
}
 

What was happening was that the static variables were being created each time you included your header. Static variables have internal linkage which means they can only be used in the file that defines them.

All I did was structure your code so that the variables were created once in the number.cpp.