通过运算符重载C ++进行字符串连接

Question

I am Unable to concatenate two strings by operator overloading. The code is given below.

  #include<iostream>
  #include<string.h>
  using namespace std;
  class String
  {
  char *len;
  public:
         String(char *s);
         void display();
         String(){}
         void setData(char *s);
         //String(String &x); 
         ~String(); 
         String operator+(String);
         void extend(int l);         
   };
   void String::extend(int f)
   {
       len=(char *)realloc(len,(f+1)*sizeof(char));
   }     
   String String::operator+(String x)
   {
     String t;
     printf("%s\n",len);
     t.setData(len);
     t.extend(strlen(len)+strlen(x.len));
     strcat(t.len,x.len);
     printf("%s\n",t.len);
     return (t);

    }       
   String::~String()
   {
       delete len;  

    }                 

  void String::setData(char *s)
  {

      len=(char *)calloc(strlen(s)+1,sizeof(char));
      strcpy(len,s);
   }     
   String::String(char *s)
   {   
       len=(char *)calloc(strlen(s)+1,sizeof(char));                
       strcpy(len,s);
   }
   void String::display()
   {
        printf("%s\n",len);
    }
  int main()
  {

    String a=String("United ");
    String b,c;
    b.setData("States");
    c=a+b;
    c.display();
    system("pause");
    return 0;
   }                                       

The Problem is that string is being concatenated inside the operator overloading function but when the object is returned and when display function is invoked then the output is garbage value.

Answer 1

Your code doesn't follow Rule Of Three . You should manually overload copy-constructor and assignment operator. Also, you SHOULN'T use delete on buffer, that was allocated by malloc / calloc / realloc , use free instead.

Answer 2

Use

<string> 

which is c++ library in place of

<string.h> 

which is ac library.

Answer 3

Able to figure out what went wrong, the definition of destructor was acting as a bugaboo. As soon as the operator function goes out of scope destructor is called and object is destroyed.

Answer 4

This code should work fine here. I know its late , but still.

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

class String
{
    char x[40];

    public:
    String() { }          // Default Constructor

    String( char s[] )
    {
        strcpy(x,s);
    }

    String( String & s )
    {
        strcpy(x,s.x );
    }

    String operator + ( String s2 )
    {
        String res;

        strcpy( res.x,x );
        strcat( res.x,s2.x);

        return(res);
    }

    friend ostream & operator << ( ostream & x,String & s );
};

ostream & operator << ( ostream & x,String & s )
{
    x<<s.x;
    return(x);
}

int main()
{
    clrscr();

    String s1="Vtu";
    String s2="Belgaum";

    String s3 = s1+ s2;      

    cout<<"\n\ns1 = "<<s1;
    cout<<"\n\ns2 = "<<s2;

    cout<<"\n\ns1 + s2 = "<<s3;

    getch();
    return 0;
}