STL Container

[lourk]

Hello Everybody!

I am a newbie in c++. I want to create a simple application that insert, search and displays data. And I am planning to use an STL Container.

What kind of STL Container am I going to use that stores 3 different data types?
example: int, bool, double

Thank you

[afraze]

lourk,

you should look over url below.

http://www.cplusplus.com/reference/stl/

After that if you have any question, we can help u..

[Darryl]

There are no Standard containers that allow multiple types. Try Boost or try using a variant or as a last resort a union

[JonLT]

or you could just use class with the three types:

class myClass
{
   public:
     int myInt;
     bool myBool;
     double myDouble;
};
 

and then use this class with a vector or the like:

std::vector<myClass> myVector;
 

or store pointers in the vector

std::vector<myClass*> myVector;
 

[weaknessforcats]

I want to create a simple application that insert, search and displays data. And I am planning to use an STL Container.

If this made sense, the STL would have a container for it. However, with multiple types (like bool, int and double) you cannot do inserts as there is no way to compare a bool to a double or a double to an int. Comparison is also involved in doing a search.

You might not even be able to display if you allow objects of multiple classes.

I think your data model is incorrect.

What is it you are trying to do??

[lourk]

Thanks for the replies.

I have use the STL Container Map that stores 2 values and it works.

Below you'll find my code:

class ContainerValues
{
public:

ContainerValues(void);
~ContainerValues(void);

void Update(long dwHandle, double dValue);
bool Remove(long Handle);
double Sum();
void Display();

private:

map<long, double>m_Map;
typedef map<long, double>::iterator IT;

};

void ContainerValues::Update(long dwHandle, double dValue)
{

Remove(dwHandle);
m_Map.insert(pair<long, double>(dwHandle, dValue));

} // end ContainerValues::Update

But I need to make it 3 values.
like: map<long, double,double>m_Map;

Then instead of pair
m_Map.insert(pair<long, double>(dwHandle, dValue));

what am I going to use since I need to make it 3 values?

Thanks

[weaknessforcats]

map<long, double>m_Map;

This does not store two values.

It stores one value. A pair.

In a map, the pair is a key/value object. That is, you find the double (a value) by asking for the long (a key).

My Post #5 still holds.

[Darryl]

Ok here is a union solution

#include <iostream>
#include <vector>
 
class multitype
{
    friend std::ostream& operator<<(std::ostream& os, const multitype& m);
 
public:
    multitype()
    {
        value.i = 0;
        type = INT;
    };
    multitype(bool in)
    {
        value.b = in;
        type = BOOL;
    }
    multitype(int in)
    {
        value.i = in;
        type = INT;
    }
    multitype(double in)
    {
        value.d = in;    
        type = DOUBLE;
    }
 
    enum TYPE {BOOL, INT, DOUBLE};
    union VALUE
    {
        bool        b;
        int        i;
        double    d;
    };
 
 
private:    
 
    VALUE value;
    TYPE type;
};
 
std::ostream& operator << (std::ostream& os, const multitype& m)
{
    switch(m.type)
    {
    case multitype::BOOL:
        return os << m.value.b;
        //return os << (m.value.b ? "true" : "false");
    case multitype::INT:
        return os << m.value.i;
    case multitype::DOUBLE:
        return os << m.value.d;
    }
}
 
 
int main()
{
    std::vector<multitype> foo;
 
    foo.push_back(20);
    foo.push_back(true);
    foo.push_back(3.14);
 
    std::cout << foo[0] << "\n" << foo[1] << "\n" << foo[2] << "\n";
 
}
 

Missing:

Test what type is being held
Assignment to the various types

[weaknessforcats]

enum TYPE {BOOL, INT, DOUBLE};
union VALUE
{
bool b;
int i;
double d;
};


private:

VALUE value;
TYPE type;

You have just recoded the Microsoft VARIANT. The code for this on an MSDN web page so just copy if off.

Again, I say, you cannot do much with containers of multi-types, like VARIANT, since the elements are incompatible with each other. You can't compare elements so you can't sort them or use a tree to access them by key, or sort, or do any ordering or assignment whatsoever.

The VARIANT was invented for Visual Basic to communicate with C functions and not for containers of VARIANT.

Discriminated unions like this are a C solution for templates.

The OP has not given the reason for needing to store 3 types in one element of a container. I expect 3 containers are what's needed.

[Darryl]

I could think of a use, like a table or spreadsheet where different cells need different types of values yet a central storage.

btw, The MS VARIANT is probably more encompassing than my implementation, I have no provision for any kind of a string.

[lourk]

I have already tried the #4 and it is now working.

Thanks to everyone for all the help.