expected constructor, destructor, or type conversion before ‘(’ token

Compiling polygone.h and polygone.cc gives error:

polygone.cc:5:19: error: expected constructor, destructor, or type conversion before ‘(’ token 

Code:

//polygone.h # if !defined(__POLYGONE_H__) # define __POLYGONE_H__ # include <iostream> class Polygone { public: Polygone(){}; Polygone(std::string fichier); }; # endif 

and

//polygone.cc # include <iostream> # include <fstream> # include "polygone.h" Polygone::Polygone(string nom) { std::ifstream fichier (nom, ios::in); std::string line; if (fichier.is_open()) { while ( fichier.good() ) { getline (fichier, line); std::cout << line << std::endl; } } else { std::cerr << "Erreur a l'ouverture du fichier" << std::endl; } } //ifstream fich1 (argv[1], ios::in); 

My guess is that the compiler is not recognising Polygone::Polygone(string nom) as a constructor, but, if this actually is the case, I have no idea why.

Any help?

4 Answers

This is not only a 'newbie' scenario. I just ran across this compiler message (GCC 5.4) when refactoring a class to remove some constructor parameters. I forgot to update both the declaration and definition, and the compiler spit out this unintuitive error.

The bottom line seems to be this: If the compiler can't match the definition's signature to the declaration's signature it thinks the definition is not a constructor and then doesn't know how to parse the code and displays this error. Which is also what happened for the OP: std::string is not the same type as string so the declaration's signature differed from the definition's and this message was spit out.

As a side note, it would be nice if the compiler looked for almost-matching constructor signatures and upon finding one suggested that the parameters didn't match rather than giving this message.

The first constructor in the header should not end with a semicolon. #include <string> is missing in the header. string is not qualified with std:: in the .cpp file. Those are all simple syntax errors. More importantly: you are not using references, when you should. Also the way you use the ifstream is broken. I suggest learning C++ before trying to use it.

Let's fix this up:

//polygone.h # if !defined(__POLYGONE_H__) # define __POLYGONE_H__ #include <iostream> #include <string> class Polygone { public: // declarations have to end with a semicolon, definitions do not Polygone(){} // why would we needs this? Polygone(const std::string& fichier); }; # endif 

and

//polygone.cc // no need to include things twice #include "polygone.h" #include <fstream> Polygone::Polygone(const std::string& nom) { std::ifstream fichier (nom, ios::in); if (fichier.is_open()) { // keep the scope as tiny as possible std::string line; // getline returns the stream and streams convert to booleans while ( std::getline(fichier, line) ) { std::cout << line << std::endl; } } else { std::cerr << "Erreur a l'ouverture du fichier" << std::endl; } } 

You are missing the std namespace reference in the cc file. You should also call nom.c_str() because there is no implicit conversion from std::string to const char * expected by ifstream's constructor.

Polygone::Polygone(std::string nom) { std::ifstream fichier (nom.c_str(), std::ifstream::in); // ... } 

You need the return type, for example "void Polygon..."