C++ headers redefining/declaring mixup

Question

I'm trying to abstract out a method from a simple program. This method tests the length of an array against a predeclared CAPACITY constant, and spits out an error message if conditions aren't met. However, I'm having trouble creating a header file with a .cpp file to hold the method.

the header file:

    //arrayHelper.h
    #ifndef ARRAYHELPER_H
    #define ARRAYHELPER_H

    void arrayLengthCheck(int & length, const int capacity, string prompt);

    #endif // ARRAYHELPER_H

the code file:

    //arrayHelper.cpp
    #include <iostream>
    #include <string>
    #include "arrayHelper.h"

    using namespace std;

    void arrayLengthCheck(int & length, const int capacity, string prompt)
    {
        // If given length for array is larger than specified capacity...
        while (length > capacity)
        {
            // ...clear the input buffer of errors...
            cin.clear();
            // ...ignore all inputs in the buffer up to the next newline char...
            cin.ignore(INT_MAX, '\n');
            // ...display helpful error message and accept a new set of inputs
            cout << "List length must be less than " << capacity << ".\n" << prompt;
            cin >> length;
        }
    }

Running this main.cpp file that contains #include "arrayHelper.h" errors out that string is not declared in the header file. Including string in the header file has no effect, but #include "arrayHelper.cpp" results in a redefinition of the method. How should I approach this problem?

Answer 1

You should #include <string> in the header, and refer to string as std::string, since using namespace std would be a bad idea in a header file. In fact it is a bad idea in the .cpp too.

//arrayHelper.h
#ifndef ARRAYHELPER_H
#define ARRAYHELPER_H

#include <string>

void arrayLengthCheck(int & length, const int capacity, std::string prompt);

#endif // ARRAYHELPER_H

Answer 2

string is used in header file but can't find the symbol.

Move #include <string> to arrayHelper.h and replace all string with std::string

Side note:

call using namespace std; locally is idiomatic way, and pass prompt by reference can elide one copy. Below is slightly enhancement to your code:

arrayHelper.h

#ifndef ARRAYHELPER_H
#define ARRAYHELPER_H

#include <string>

void arrayLengthCheck(int & length, const int capacity, const std::string& prompt);

#endif // ARRAYHELPER_H

arrayHelper.cpp

#include <iostream>
#include "arrayHelper.h"

void arrayLengthCheck(int & length, const int capacity, const std::string& prompt)
{
   using namespace std;    

    // If given length for array is larger than specified capacity...
    while (length > capacity)
    {
        // ...clear the input buffer of errors...
        cin.clear();
        // ...ignore all inputs in the buffer up to the next newline char...
        cin.ignore(INT_MAX, '\n');
        // ...display helpful error message and accept a new set of inputs
        cout << "List length must be less than " << capacity << ".\n" << prompt;
        cin >> length;
    }
}

Answer 3

You need to say std::string in your header file...