function not declared in this scope error with c++ header

I'm getting an error that says: this function was not declared in this scope error with g++ compiler.
** Error message at the end of the question.**

I'm trying to make a separete header file for my simple program. For this I created a new class called mread and kept it in the header file. Being new to c++ and after extensive searches online, I figured out how to correctly configure header files. But on my way to learning I might have missed some importand concepts.

So here's my entire code:

main.cpp

#include"mread.h"

using namespace std;
//function prototypes
int main(int argc,char* argv[])
{

   //if invalid command format used.
   if(argc!=2)
   {
      cout<<"Please enter the correct command format: "<<"\n";
      cout<<argv[0]<<" <filename>"<<"\n";
      return 1; 
   }
   //initialize all required variables
   string mbox = argv[1];
   ifstream reader; 

   reader.open(mbox.c_str()); // stream the file to the ifstream 'reader'

   if(!reader) // check if the file does exist
   {
      cerr<<"Sorry,the file:"<< mbox<<" is not in this directory."<<"\n";
      reader.close();
      return 1;
   }

   list<string> data_container;
   mread::read_messages(data_container,reader); 
   data_container.sort();
   /*
   sorting the contents of the the list using the linked list actually sorts 
   even the numeric strings without having to extract them as numbers
   */
   mread::show_messages(data_container);
   return 0;
}

mread.cpp

#include"mread.g"
// this function returns the message number in string format
string mread::get_pkt_num(string message) 
{
   string ch = message.substr(0,3); // extract the interpart from the message
   return ch;   
}
//this function decapsulates the message from the packets and returns it
string mread::extract_message(string message)
{
   int len = message.length();
   message = message.substr(8,len);
   return message;
}
void mread::show_messages(list<string> &packet)
{
   list<string>::iterator itr;
   string pkt_num="0";
   for(itr=packet.begin();itr!=packet.end();itr++) // iterate through the list
   {
      if(pkt_num=="0") //this checks for the first message
      {
         pkt_num = get_pkt_num(*itr);
         cout<<"\n"<<"Message "<<pkt_num<<"\n";
      }
      // change a new line and move on to another line for a new message
      if(get_pkt_num(*itr)!=pkt_num && pkt_num!="0")
      {
         pkt_num = get_pkt_num(*itr);
         cout<<"\n"<<"Message "<<pkt_num<<"\n";
      }
      cout<<"\t"<<extract_message(*itr); 

   }
}
void mread::read_messages(list<string>&packet,ifstream& reader)
{
   string temp; 
   char ch;
   while(!reader.eof()) //iterate until the reader reaches the EOF.
   {
      reader.get(ch);
      temp=temp+ch;
      if(ch=='\n') //condition to check for end of each line
         {
            //store the string retrieved till now and set the temp to NULL
            packet.push_back(temp);
       s     temp.clear();
         }
         /*
         if end of message reached before reaching the EOF,then break the loop.
         Everything after the END will be discarded even if there was a message.
         */
         if(temp=="END") 
         {  
            break;
         }
   }
   reader.close();
}

and finally, the mread.h file:

#ifndef _mread_
#define _mread_

#include<iostream>
#include<string>  
#include<fstream> // library for reading and writing files
#include<list>  // for using list data types
#include<stdlib.h>
using namespace std;
public class mread
{

void mread()
{
};
public string get_pkt_num(string);
public string extract_message(string);
public void show_messages(list<string> &);
public void read_messages(list<string>&,ifstream&);

};
#endif  

I'm using g++ compiler and whenever I try to compile the code with
g++ main.cpp , I get two errors:

main.cpp: In function ‘int main(int, char**)’:
main.cpp:42: error: ‘read_messages’ was not declared in this scope
main.cpp:48: error: ‘show_messages’ was not declared in this scope

I'm new to c++. Please Help.