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

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 J�rgensen -- --------------------------------------------------------------------------- Home of Martin J�rgensen - http://www.martinjoergensen.dk

"Martin J�rgensen" <unoder.spam@spam.jay.net> wrote in message news:4jpui3-2j1.ln1@news.tdc.dk > 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 J�rgensen > > -- > --------------------------------------------------------------------------- > Home of Martin J�rgensen - http://www.martinjoergensen.dk

Martin Jørgensen 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 Jørgensen >

Martin J�rgensen wrote: > 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 http://c2.com/cgi/wiki?ZeekLand <-- NOT a blog!!!

Phlip wrote: >> 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. 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! -- Phlip http://c2.com/cgi/wiki?ZeekLand <-- NOT a blog!!!

John Carson wrote: > "Martin J�rgensen" <unoder.spam@spam.jay.net> wrote in message > news:4jpui3-2j1.ln1@news.tdc.dk > >>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). Thanks! Problem solved. Best regards / Med venlig hilsen Martin J�rgensen -- --------------------------------------------------------------------------- Home of Martin J�rgensen - http://www.martinjoergensen.dk