Map to store 3 items

[Brad]

New to C++. Just ran into a need to store three things in a map. Before
trying it, I thought I'd post here and ask for advice. Here is an
example of what I need to store:

map<string name, string prefix, int length>

Both name and prefix would be unique for each map entry. I was wondering
if the the first entry could be an array that holds the two items (name
and prefix), but then I wondered how an iterator would behave when
it->first is called.

Any suggestions or pointers on using a map with three items would be
much appreciated.

Brad

[Jerry Coffin]

In article <fv**********@solaris.cc.vt.edu>, br**@16systems.com says...

New to C++. Just ran into a need to store three things in a map. Before
trying it, I thought I'd post here and ask for advice. Here is an
example of what I need to store:

map<string name, string prefix, int length>

Both name and prefix would be unique for each map entry. I was wondering
if the the first entry could be an array that holds the two items (name
and prefix), but then I wondered how an iterator would behave when
it->first is called.

It can't be an array -- it has to be copyable and assignable. It can be
a pair<string, stringthough, in which case you'd do something like
it->first.first or it->first.second, to access the name and prefix
respectively.

Of course, you could also create a class of your own to hold the two
strings, something like:

class key {
string name;
string prefix;
public:
key(string n, string p) : name(n), prefix(p) {}
key(key const &other) : name(other.name), prefix(other.prefix) {}
key &operator=(key const &other) {
name = other.name;
prefix = other.prefix;
return *this;
}

bool operator<(key const &other) const {
if (name < other.name)
return true;
if (name other.name)
return false;
if (prefix < other.prefix)
return true;
return false;
}
};

--
Later,
Jerry.

The universe is a figment of its own imagination.

[=?utf-8?Q?David_C=C3=B4me?=]

On Thu, 08 May 2008 03:26:03 +0200, Brad <br**@16systems.comwrote:

New to C++. Just ran into a need to store three things in a map. Before
trying it, I thought I'd post here and ask for advice. Here is an
example of what I need to store:

map<string name, string prefix, int length>

Both name and prefix would be unique for each map entry. I was wondering
if the the first entry could be an array that holds the two items (name
and prefix), but then I wondered how an iterator would behave when
it->first is called.

Any suggestions or pointers on using a map with three items would be
much appreciated.

Brad

Boost Tuple ?

[Juha Nieminen]

Jerry Coffin wrote:

class key {
string name;
string prefix;
public:
key(string n, string p) : name(n), prefix(p) {}
key(key const &other) : name(other.name), prefix(other.prefix) {}
key &operator=(key const &other) {
name = other.name;
prefix = other.prefix;
return *this;
}

What exactly do you need that copy constructor and assignment operator
for? They are doing exactly what the default ones would do. They are
useless.

How about simply:

struct Key
{
std::string name, prefix;

Key(std::string& n = "", std::string p = ""): name(n), prefix(p) {}

bool operator<(const Key& rhs)
{
return name == rhs.name ? prefix < rhs.prefix : name < rhs.name;
}
}

[Jerry Coffin]

In article <2Q*************@read4.inet.fi>, no****@thanks.invalid
says...

[ ... ]

What exactly do you need that copy constructor and assignment operator
for? They are doing exactly what the default ones would do. They are
useless.

You're right -- I should have pointed out that I was including them only
for emphasis, but they're only doing what the compiler would generate if
they weren't included.

--
Later,
Jerry.

The universe is a figment of its own imagination.