Re: compilation error: "error: no matching function for call to 'String::String(String)'

From:
Rolf Magnus <ramagnus@t-online.de>
Newsgroups:
comp.lang.c++
Date:
Sat, 06 May 2006 17:12:56 +0200
Message-ID:
<e3iedo$rci$00$1@news.t-online.com>
Martin JQrgensen wrote:

Hello again,

Sorry to bother but I guess my C++ book isn't very good since it
obviously contains errors so the program code doesn't work with g++.

However I don't understand what the problem is. Last time the problem
was that "using namespace std" apparently had a "link" class/object
defined already. Now I get:

error: no matching function for call to 'String::String(String)'

See if you can spot the error because I can't:


Well, it would have be much easier to spot if you had included the line
number or better even marked the line that produced the error.

- - - - - - - - - - - - - - -
// memory-saving String class
// overloaded assignment and copy constructor
#include <iostream>
#include <cstring> //for strcpy(), etc.
using namespace std;
////////////////////////////////////////////////////////////////
class strCount //keep track of number
{ //of unique strings
private:
     int count; //number of instances
     char* str; //pointer to string
     friend class String; //make ourselves available
                                 //member functions are private

 
//--------------------------------------------------------------
     strCount(char* s) //one-arg constructor
         {
         int length = strlen(s); //length of string argument
         str = new char[length+1]; //get memory for string
         strcpy(str, s); //copy argument to it
         count=1; //start count at 1
         }
     //--------------------------------------------------------------
     ~strCount() //destructor
         { delete[] str; } //delete the string
};
////////////////////////////////////////////////////////////////
class String //String class
{
private:
     strCount* psc; //pointer to strCount
public:
     String() //no-arg constructor
     { psc = new strCount("NULL"); }
     //--------------------------------------------------------------
     String(char* s) //1-arg constructor
     { psc = new strCount(s); }
     //--------------------------------------------------------------
     String(String& S) //copy constructor


Here is probably the problem. Your copy constructor claims to modify the
original string, because the parameter is a non-const reference. Try:

      String(const String& S) //copy constructor

Since your whole program doesn't care about const-correctness, I guess
that's the point where your book is failing.

     {
         psc = S.psc;
         (psc->count)++;
     }
     //--------------------------------------------------------------
     ~String() //destructor
     {
         if(psc->count==1) //if we are its last user,
             delete psc; // delete our strCount
         else // otherwise,
             (psc->count)--; // decrement its count
     }
     //--------------------------------------------------------------
     void display() //display the String
     {
         cout << psc->str; //print string
         cout << " (addr=" << psc << ")"; //print address
     }
     //--------------------------------------------------------------
     void operator = (String& S) //assign the string
     {
         if(psc->count==1) //if we are its last user,
             delete psc; // delete our strCount
         else // otherwise,
             (psc->count)--; // decrement its count
         psc = S.psc; //use argument's strCount
         (psc->count)++; //increment its count
     }
};
////////////////////////////////////////////////////////////////
int main()
{
     String s3 = "When the fox preaches, look to your geese.";
     cout << "\ns3="; s3.display(); //display s3

     String s1; //define String
     s1 = s3; //assign it another String
     cout << "\ns1="; s1.display(); //display it

     String s2(s3); //initialize with String
     cout << "\ns2="; s2.display(); //display it
     cout << endl;
     return 0;
}

- - - - - - - - - - - - - - -

I didn't make the comments. I just copy/pasted the code so I don't want
to spend time on removing them as I also find it okay that they're there.

Best regards / Med venlig hilsen
Martin JQrgensen

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