design a string class constructor c++

Question

what is the best way to design a string class constructor? The following constructors definitely have problem: two pointers pointing one object, if one of them is destructed, the other will cause a fatal error. So, what is the best way to design a constructor for a string class?

class CMyString{
    private:
        char *pData;
    public:
        CMyString(char *_p=NULL):pData(_p){
    }
        CMyString(CMyString &_str):pData((_str.pData){
    }
}

All of the string objects I have ever designed have MULTIPLE constructors that allow users to input differing data types into the string. — trumpetlicks
– trumpetlicks, Commented Feb 25, 2014 at 22:36
Since your class doesn't have a destructor, your statement is patently false. — Kerrek SB
– Kerrek SB, Commented Feb 25, 2014 at 22:42

Vlad from Moscow · Accepted Answer · 2014-02-25 22:55:41Z

For example you can define the class the following way.

class CMyString
{
private:
    char *pData;

public:
    CMyString( const char *_p = NULL )
    {
        if ( _p == NULL ) 
        {
            pData = NULL;
        }
        else
        {
            pData = new char[ std::strlen( _p ) + 1 ];
            std::strcpy( pData, _p );
        }
    }

    CMyString( const CMyString &_str )
    {
        if ( _str.pData == NULL ) 
        {
            pData = NULL;
        }
        else
        {
            pData = new char[ std::strlen( _str.pData ) + 1 ];
            std::strcpy( pData, _str.pData );
        }
    }

    explicit operator bool () const { return ( pData != NULL ); } 

    CMyString & operator =( const CMyString & ); // do not forget to define

    ~CMyString(); // do not forget to define
};

Or you can define the copy constructor the following way

    CMyString( const CMyString &_str ) : CMyString( _str.pData )
    {
    }

Brian Bi · Accepted Answer · 2014-02-25 22:39:26Z

1

Allocate space and copy the characters over.

Also, I suggest not allowing pData to be null, as it complicates the logic. Instead, if no initial value is given, create an empty string.

Also, don't forget to be const-correct.

CMyString(const char *_p = "") {
    size_t len = strlen(_p);
    pData = new char[len+1];
    strcpy(pData, _p);
}
CMyString(const CMyString& _str) { /* basically the same as above */ }

answered Feb 25, 2014 at 22:39

Brian Bi

123k13 gold badges197 silver badges353 bronze badges

7 Comments

Spock77 Over a year ago

CMyString myStr(0); will crash this

trumpetlicks Over a year ago

I also disagree with your statement about pData to be null. It is a very real possibility that a user could indeed pass in an un-initialized char * _p, and this case should be handled. It DOES complicated the logic, but it is NECESSARY complication, when coding SAFE code.

Brian Bi Over a year ago

@Alex passing in an unterminated string could also crash it. So what? You just tell your users not to do it.

Brian Bi Over a year ago

@trumpetlicks See my comment above.

Spock77 Over a year ago

I prefer programs that do not crash totally when smb forget to initialize char*. Passing 0 is happening quite often. Yes, std::string does not check and will crash also. But I would prefer SafeString which checks possible errors. Why you think MS implemented a set of *s safe functions? They could just tell their users not to use it wrong way. But the problem is that users _do.

|

Collectives™ on Stack Overflow

design a string class constructor c++

2 Answers 2

Comments

7 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

7 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related