trouble with passing a string pointer and then checking size in a constructor/method

Question

I'm still learning about strings, but I'm trying to use them more often. How could I get something like this to work? I'm not even sure where to start (yes, this is an object. I'm also learning about these atm for an assignment)

MyClass::MyClass(string* newName)
{
  if (newName.length() > maxNameLength) //maxNameLength = 50
  {  
     //do stuff
  }
}

You do not need the pointer bit - try `MyClass::MyClass(const std::string& newName)` — Ed Heal, Feb 06 '16 at 10:20
That seemed to work, thank you. Now I have to try and understand why. — Robolisk, Feb 06 '16 at 10:22

Anedar · Answer 1 · 2016-02-06T10:31:54.130

3

As an alternative to Ed's answer:

If you really want to use a pointer, your constructor should look like this:

MyClass::MyClass(const std::string* const newName)
{
  if (newName!=nullptr && newName->length() > maxNameLength) //maxNameLength = 50
  {  
    //do stuff
  }
}

Not the operator-> to call length(). You can skip one of the const qualifiers if you either need to change the pointer or its content.

Anyway, using references is usually the better alternative.

edited Feb 06 '16 at 10:31

answered Feb 06 '16 at 10:29

Anedar

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The problem is - What happens if you pass a null pointer? Better to have the compiler pick that one up – Ed Heal Feb 06 '16 at 10:30
good point, added that. As i said, using references is usually the better way to do this.... – Anedar Feb 06 '16 at 10:32
Perhaps an `assert`? – Ed Heal Feb 06 '16 at 10:33
Since the OP didn't give us any information about his actions if the string exceeds maxLength, i just decided to check for nullptr and if so to not "//do stuff" – Anedar Feb 06 '16 at 10:44

score 2 · Accepted Answer · answered Feb 06 '16 at 10:25

2

Here is a little explanation as to use

MyClass::MyClass(const std::string& newName)

You do not need a pointer to the string. A reference is better - hence &
Your constructor should not be modifying this string - tell both the compiler and the developer - hence const
Do not pollute your namespace - hence std::
DO NOT USE using std (see 3)

answered Feb 06 '16 at 10:25

Ed Heal

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can you explain exactly this namespace std stuff? I found that I don't always put "std::string str1" just "string str1", is that bad practice? and if so, should I be using a char. As you can imagine, my class has a private data member that is "string name", hence why I'm calling my constructor to change it. – Robolisk Feb 06 '16 at 10:36
1

If you are able to do `string str1` then somewhere somebody (maybe you) has a line `using std`. This pollutes the namespace as it includes a lot of stuff. See http://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice etc – Ed Heal Feb 06 '16 at 10:39

trouble with passing a string pointer and then checking size in a constructor/method

2 Answers2