Question

I am new to this website and I am trying a simple inheritance example in C++.
I checked my code lots of times and I really see nothing wrong with it, however the compilers gives me errors:

my code:

#ifndef READWORDS_H
#define READWORDS_H
using namespace std;
#include "ReadWords.h"

/**
 * ReadPunctWords inherits ReadWords, so MUST define the function filter.
 * It chooses to override the default constructor.
 */

class ReadPunctWords: public ReadWords {
    public:
    bool filter(string word);
};

#endif

And the messages I get from the compiler:

ReadPunctWords.h:11: error: expected class-name before '{' token
ReadPunctWords.h:13: error: `string' has not been declared
ReadPunctWords.h:13: error: ISO C++ forbids declaration of `word' with no type

Tool completed with exit code 1

I am really not sure where I get it wrong as it looks just fine to me?
Thank you for any mistakes you might spot.

Answer 1

You need to include string:

#include <string>

That said, don’t use using namespace! Especially at file-scope, and definitely not in a header file. Now any unit that includes this file is forced to succumb to everything in the std namespace.

Take that out, and qualify your names:

bool filter(std::string word);

It’s arguable more readable, too. Additionally, you should take your string as a const&:

bool filter(const std::string& word);

To avoid having to copy the string unnecessarily. Lastly, your header guards seem off. Should they be changed? As of now, they seem like the same ones that would be used in your other header, which might effectively stop it from being included.

If you define READWORDS_H and then include ReadWords.h, and if that also has:

#ifndef READWORDS_H
#define READWORDS_H

Then nothing in that file will be processed. If that’s the case, ReadWords as a class won’t be defined, and you cannot inherit from it. Your guard should probably be:

READPUNCTWORDS_H