Initialize character arrays in class

Question

When I compile the code below with g++ 4.8.2 I get an error.

#include <iostream>

using namespace std;

class test {
public:
    void print() {
        cout << str << endl;
    }

private:
    char str[] = "123456789"; // error: initializer-string for array of chars
                              // is too long
};

int main() {
    char x[] = "987654321";
    cout << x << endl;

    test temp;
    temp.print();
}

Why did I get that error, what is the difference between str in class test and x in main function?

Answer 1

Inside your class, you have to explicitly specify the array size:

class test {
...
private:
    // If you really want a raw C-style char array...
    char str[10] = "123456789"; // 9 digits + NUL terminator
};

Or you can simply use a std::string (which I think is in general much better in C++ code than using raw C-style strings):

#include <string>
...

class test {
...
private:
    std::string str = "123456789"; 
};

Answer 2

You can't have arrays of unknown size in structures/classes, you need to set an array size.

Or better yet, use std::string for strings. It's what it's made for.

Answer 3

I realised what you are asking and rewrite my entire reply. You are not supposed to do you initialization in your class. You only declare the variables/methods you want to use. Only after that, you use your class to create objects.

Set the object's variable's value from then on.

For example:

class Test
{
   public:
        int num;    //You don't intialie value here
};

int main
{
       Test testObj();
       testObj.num = 100;
}

However, if you set the variables to private, you need to create a function in your class to access the class members. For exmaple setNum()

Alternatively, you can set the variables using the constructor, and insert it as parameter inputs during object creation.

class Test
{
   public:
        Test(int);  //Constructor
   private:
        int num;    //You don't intialie value here
};


Test::Test(int value)
{
    this -> num = value;
}

int main
{
    Test testObj(100); //set num to 100
}

If you want to access it using class member function, you can do this, but of course you have to define setNum() in your class first.

testObj.setNum(100);

I know you are asking about char[], but I am giving you example on int. That is not the problem in your code. Either int or char[], you should avoid declaring it directly in your class. It seems like the main problem with your code is not whether you are using char[] or char*. You should not initialize your values in your class.