Ordering

[Ness]

I have a project that I'm working on, and it concerns a mass userbase. I ave a structure containing information about each user. There is one variable, priority, which is self explainatory. What I want to do is organize each one by higher priority. Like the dude with highest priority is [0], then 2nd highest [1]. How can I do this?

[kuphryn]

One solution is an STL container such as a set.

Kuphryn

[Yasoo]

I would have have an array of structures and then use qsort()

Yasoo
Z++ Technologies

[Ness]

But the number is inside the structure.

typedef struct user_tag
{
     int priority;
} user;

user users[2000];

[Yasoo]

Check out the docs for qsort. One of the arguments is:

int (__cdecl *compare )(const void *elem1, const void *elem2 )

This is the function that you create which qsort calls to do the comparison. In that function you would do something like:

if ( ((struct user_tag *)elem1)->priority > ((struct user_tag *)elem2)->priority )
    return 1;
else if ( ((struct user_tag *)elem1)->priority < ((struct user_tag *)elem2)->priority )
    return -1;
else
    return 0;

Yasoo
Z++ Technologies

[Paul McKenzie]

Originally posted by Ness
But the number is inside the structure.

typedef struct user_tag
{
     int priority;
} user;

user users[2000];

Is this C or C++? If it's C++, there is std::sort. Also, the typedef is not needed for C++.

#include <algortihm>

struct user
{
   int priority;
};

bool SortByPriority( const user& first, const user& second)
{
   return first.priority < second.priority;
}

int main()
{
   user users[1000];
   //...
   std::sort( users, users + 1000, SortByPriority );
}

Qsort may work, but using std::sort is the preferred way to do this for C++ programs (note that there are no casts necessary whatsoever for std::sort).

Regards,

Paul McKenzie

[Paul McKenzie]

Originally posted by Yasoo
I would have have an array of structures and then use qsort()

Yasoo
Z++ Technologies

I agree with the array of structures, but if it is a C++ program, usage of std::sort is preferred over qsort for many reasons.

Regards,

Paul McKenzie

[Ness]

When I use std::sort, it just clears my whole array, leaving absolutly nothing in it. What's wrong?

[Ness]

*bump bump bump*

[gstercken]

When I use std::sort, it just clears my whole array, leaving absolutly nothing in it. What's wrong?

How can we know without seeing your code using std::sort?

[Kheun]

How about using a priority queue.

[Ness]

This is my complete structure (replace priority with coins):

typedef struct user_tag
{
	char username[13];
	char password[13];
	char NAME[13];
	char ip[17];
	char avatar[500];
	char location[25];

	int usernumber;
	int wins;
	int lost;
	int games;
	int percentofwin;
	int coins;

	bool login;
	int acceptNumber;

	int track[16];
} user;

user users[2000]

And here's the complete code:

bool SortByPriority( const user& first, const user& second)
{
   /*if(first.coins == second.coins)
   {
	   return first.usernumber < second.usernumber;
   }
   else
   {
	   return first.coins < second.coins;
   }*/

	return first.coins < second.coins;
}

// another function...

	std::sort( users, users + 2000, SortByPriority );

I fill the structures before I sort them. What's wrong now?

[Philip Nicoletti]

std::sort( users, users + 2000, SortByPriority );

Are there actually 2000 elements in the array ? I know 2000
is the dimension of the array, but how much of the array do
you actually use ? The "2000" in the code above should be
the actual number of elements that have been given values.

[Ness]

Thanks a bunch, but theres ANOTHER problem. How do I make it sort grom greatest to least?

[Philip Nicoletti]

The SortByPriority() function determines how the elements
are sorted. You can change it to sort any way you want :

bool SortByPriority( const user& first, const user& second)
{
	return first.coins > second.coins; // largest to smallest
}