CODEWITHSUNDEEP
c++visual-studio-2013copy-constructorlinker-errorsdefault-copy-constructor
Tugal.44
Tugal.44

Reputation: 153

copy-constructors and linking errors

Let's take this snippet code :

class MyClass
{
public:
    int m_num;
    MyClass(int n) { m_num = n;}
}

If I create an object of this class the following way :

MyClass mc1(5);
MyClass mc2(mc1);

This calls to the default copy-constructor and it'll automatically assign mc2.m_num = mc1.m_num ? Also if there's a call inside the class which makes an instance the following way :

MyClass mc3(*this);

This will call to the default copy-constructor same as with mc2 the *this is just getting the object itself to be copied ?

Second problem I'm having is with compiling my code with Microsoft Visual Studio 2013. I've made a String class and when I try to compile I get lot's of linking error telling me that the functions are already defined for some reason. String.h :

#pragma once
class String
{
private:
    char* m_szStr;
    unsigned int m_length;
public:
    String(const char*);
    explicit String(unsigned int);
    String(const String&);
    ~String();
    String& operator=(const String&);
    bool operator==(const String&) const;
    String operator+(const String&) const;
    operator const char*() const;
    int findStr(char*) const;
    int getLen() const;
    void copyStr(const char*);

};

String.cpp:

#include "stdafx.h"
#include "String.h"

String::String(const char* pch)
{
    m_szStr = NULL;
    copyStr(pch);
}

String::String(unsigned int len)
{
    m_length = len;
    m_szStr = new char[m_length];
}

String::String(const String& that)
{
    copyStr(that.m_szStr);
}

String::~String()
{
    delete[] m_szStr;
}

String& String::operator=(const String& that)
{
    copyStr(that.m_szStr);
    return *this;
}

bool String::operator==(const String& that) const
{

    if (m_length != that.m_length)
        return false;
    for (unsigned int i = 0; i < m_length; i++)
    {
        if (m_szStr[i] != that.m_szStr[i])
            return false;
    }
    return true;
}

String String::operator+(const String& that) const
{
    String temp(m_length + that.m_length - 1);
    unsigned int offset = m_length;
    for (unsigned int i = 0; i < that.m_length; i++)
    {
        temp.m_szStr[offset] = that.m_szStr[i];
    }
    return temp;
}

String::operator const char*() const
{
    return m_szStr;
}

int String::findStr(char* pch) const
{
    unsigned int offset = 0;
    unsigned int strIndex = -1;
    for (unsigned int i = 0; m_szStr[i] != NULL && pch[offset] != NULL; i++)
    {
        if (m_szStr[i] == pch[offset])
        {
            if (strIndex == -1)
                strIndex = i;
            offset++;
        }
        else
        {
            strIndex = -1;
            offset = 0;
        }
    }
    return strIndex;
}

int String::getLen() const
{
    unsigned int len = 0;
    for (unsigned int i = 0; m_szStr[i] != NULL; i++)
    {
        len++;
    }
    return len;
}

void String::copyStr(const char* pch)
{
    if (!m_szStr)
        delete[] m_szStr;
    unsigned int pchLen = 0;
    for (unsigned int i = 0; pch[i] != NULL; i++)
    {
        pchLen++;
    }
    m_length = pchLen;
    m_szStr = new char[m_length];
    for (unsigned int i = 0; i < m_length; i++)
    {
        m_szStr[i] = pch[i];
    }
}

Code file:

#include "stdafx.h"
#include <iostream>
#include "String.cpp"

using namespace std;


int _tmain(int argc, _TCHAR* argv[])s
{
    String s1("Hi!");
    String s2(5);
    s2 = "Hello, Hi!";
    const char* pch = static_cast<const char*>(s2);
    cout << pch << endl;
    return 0;
}

errors:

Error   1   error LNK2005: "public: __thiscall String::String(class String const &)" (??0String@@QAE@ABV0@@Z) already defined in assignment4.obj    C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   2   error LNK2005: "public: __thiscall String::String(unsigned int)" (??0String@@QAE@I@Z) already defined in assignment4.obj    C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   3   error LNK2005: "public: __thiscall String::String(char const *)" (??0String@@QAE@PBD@Z) already defined in assignment4.obj  C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   4   error LNK2005: "public: __thiscall String::~String(void)" (??1String@@QAE@XZ) already defined in assignment4.obj    C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   5   error LNK2005: "public: class String & __thiscall String::operator=(class String const &)" (??4String@@QAEAAV0@ABV0@@Z) already defined in assignment4.obj  C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   6   error LNK2005: "public: bool __thiscall String::operator==(class String const &)const " (??8String@@QBE_NABV0@@Z) already defined in assignment4.obj    C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   7   error LNK2005: "public: __thiscall String::operator char const *(void)const " (??BString@@QBEPBDXZ) already defined in assignment4.obj  C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   8   error LNK2005: "public: class String __thiscall String::operator+(class String const &)const " (??HString@@QBE?AV0@ABV0@@Z) already defined in assignment4.obj  C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   9   error LNK2005: "public: void __thiscall String::copyStr(char const *)" (?copyStr@String@@QAEXPBD@Z) already defined in assignment4.obj  C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   10  error LNK2005: "public: int __thiscall String::findStr(char *)const " (?findStr@String@@QBEHPAD@Z) already defined in assignment4.obj   C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   11  error LNK2005: "public: int __thiscall String::getLen(void)const " (?getLen@String@@QBEHXZ) already defined in assignment4.obj  C:\Users\****\Desktop\C++ Programming\assignment4\assignment4\String.obj    assignment4
Error   12  error LNK1169: one or more multiply defined symbols found   C:\Users\****\Desktop\C++ Programming\assignment4\Debug\assignment4.exe 1   1   assignment4

Upvotes: 0

Views: 707

Answers (1)

Christophe
Christophe

Reputation: 73376

In your main code file, write: 

#include "String.h"   // with .cpp you redefine everything !!

Currently you include String.cpp. So in your main file you will redefine everything you have already defined in String.cpp. It will compile, but the linker will be confused because he will find a definition for your String member functions in String.obj as well as in main.obj ("one definition rule").

And you already answerd yourself your copy constructor question

Upvotes: 2

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