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

[=?ISO-8859-1?Q?Martin_J=F8rgensen?=]

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:

- - - - - - - - - - - - - - -
// 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
{
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 Jørgensen

 

[John Carson]

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:

Change the String copy contructor to take a const reference rather than a
plain reference (copy constructors should always take const references).


--
John Carson

- - - - - - - - - - - - - - -
// 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
{
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 Jørgensen

 

[Rolf Magnus]

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.

 

[Phlip]

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

Get /Accelerated C++/ by Koenig and Moo, so you can skip over these
low-level issues and learn to write useful programs sooner. And read more
than 3 tutorials.

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:

And that's a reason not to use 'using namespace std'.

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

On what line? Next time comment such a line with // <-- error

String(String& S) //copy constructor

Make that String(String const & S). Without the 'const', the compiler
automatically generates another copy constructor for you, with the signature
String(String const & S). Then on this line...

String s2(s3); //initialize with String

....the compiler can't disambiguate the two calls, or something.

 

[Phlip]

Make that String(String const & S). Without the 'const', the compiler
automatically generates another copy constructor for you, with the
signature String(String const & S). Then on this line...


...the compiler can't disambiguate the two calls, or something.

Reviewing the other two posts, I now realize I was the closest to the
answer. Strike "or something".

When a compiler can't disambiguate two calls, it declares that it can't find
the simplest thing that it was looking for. For example:

void foo(short x);
void foo(long x);
foo(10); // <-- will report a missing foo(int)

So the simplest thing it can infer from String s2(s3) is
String::String(String). So the error message asks for that constructor,
instead of the canonical String::String(String const &).

(Despite String::String(String) is an impossible constructor, which is an
unrelated point. If you wrote a copy constructor without any &, then s3
would call that copy constructor to copy into the parameter argument. And
that would recursively call the same copy constructor forever.)

I win!

 

[=?ISO-8859-1?Q?Martin_J=F8rgensen?=]

Change the String copy contructor to take a const reference rather than a
plain reference (copy constructors should always take const references).

Thanks! Problem solved.


Best regards / Med venlig hilsen
Martin Jørgensen