method declared in struct in C++ (STL)

Question

I'm trying to understand the syntax used in STL for a class. Our teacher pointed us to this website (http://www.sgi.com/tech/stl/Map.html) where I copied the code below:

struct ltstr
{
  bool operator()(const char* s1, const char* s2) const
  {
    return strcmp(s1, s2) < 0;
  }
};

int main()
{
  map<const char*, int, ltstr> months;

  months["january"] = 31;
  months["february"] = 28;
  months["march"] = 31;
  months["april"] = 30;
  months["may"] = 31;
  months["june"] = 30;
  months["july"] = 31;
  months["august"] = 31;
  months["september"] = 30;
  months["october"] = 31;
  months["november"] = 30;
  months["december"] = 31;

  cout << "june -> " << months["june"] << endl;
  map<const char*, int, ltstr>::iterator cur  = months.find("june");
  map<const char*, int, ltstr>::iterator prev = cur;
  map<const char*, int, ltstr>::iterator next = cur;    
  ++next;
  --prev;
  cout << "Previous (in alphabetical order) is " << (*prev).first << endl;
  cout << "Next (in alphabetical order) is " << (*next).first << endl;
}

I did not know you could declare methods in structs. How does that work?

I'm assuming that with it, when you declare the map named months, using the luster in the Compare field of a map alphabetizes the map. But still unsure about how it works with the struct syntax. Thanks.

Martin B · Accepted Answer · 2010-07-15 13:51:24Z

15

In C++, a struct is really just a class whose default access specifier is public and which inherits publicly by default.

In other words,

struct ltstr
{
    // ...
};

is equivalent to

class ltstr
{
public:
    // ...
};

If you want to, you can make parts of your struct protected or private, too.

The reason that struct is still in C++, even though it's redundant, is backwards compatibility.

edited Jul 15, 2010 at 13:51

answered Jul 15, 2010 at 13:35

Martin B

24.3k7 gold badges55 silver badges73 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Martin B Over a year ago

@Alexandre: Good point -- I've incorporated this into the answer.

Martin B Over a year ago

@Alexandre: Oooops... should have checked. This means the two code snippets are not just almost equivalent but exactly equivalent...

onof · Accepted Answer · 2010-07-15 13:57:32Z

1

in C++ structs are classes with public members by default

edited Jul 15, 2010 at 13:57

answered Jul 15, 2010 at 13:35

onof

17.4k7 gold badges52 silver badges86 bronze badges

3 Comments

corsiKa Over a year ago

You mean, with public members by default

user322610 Over a year ago

And inherit as public by default.

Björn Pollex Over a year ago

-1 This wrong. The comments have it right, and I will remove my downvote if you edit your answer.

mahju · Accepted Answer · 2010-07-15 13:38:45Z

0

The struct does not add any functionality compared to a class except defaulting on public members. As such, none of that functionality is struct specific.

answered Jul 15, 2010 at 13:38

mahju

1,1561 gold badge14 silver badges21 bronze badges

Collectives™ on Stack Overflow

method declared in struct in C++ (STL)

3 Answers 3

2 Comments

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related