dereived class

[mar11]

Hi,

I want to derive a class from the main class as shown in the code below. But I am not sure how can I deal with the constructors of both classes.

// erasing from map
#include <iostream>
#include <string>
#include <queue>
#include <stdio.h>
#include <sstream>
using namespace std;


class ma
{
  ma(string st);
};

class sub
 :public ma
{
public:
 sub(string a);
};

int main ()
{

std::string st = "hello";
queue<sub*> test;

test.push(new sub(st));

  return 0;
}

If I compile the this code I got this error message:
/tmp/ccQvbxR8.o: In function `main':

test.cpp:(.text +0xf6): undefined reference to `sub::sub(std:: basic_string<ch ar, std::char_trait s<char>, std::allocator< char> >)'
collect2: ld returned 1 exit status

May someone please help!!

Regards

[MartijnHoekstra]

you should implement (declare) the constructors.
Now they are just definitions.

the sub could look like:

class sub :public ma 
{ 
public: 
 sub(string a) : ma(a) {} 
};

[weaknessforcats]

you should implement (declare) the constructors.
Now they are just definitions.

When you implement a function, that is when you code it, that is a definition.

When you code a function prototype, that is a declaration.