This function might help you:

Thanks guys! Now I have one idea! I'm going to make variables for the characters top, bottom, left and right and a function for the other objects with the same idea.
Then I'm going to check if the characters bottom value is smaller then the objects top value and if true it can walk and the same idea for all sides But then the character can't pass the top value of the objects, like if I want to go on the right side of the character. How should I do that?

A suggestion if you want to go with circular collisions as TeamTerradactyl suggested

Don't use sqrt(), it can become a bottle neck for the code, instead of taking the square root of the two squares, square what you are comparing it to.

(distance ^ 2) < (a^2 + b^2)

and save on the sqrt() call, also ^ in c/c++ is the xor operator, not power of, so you will have to go

(distance * distance) < ((a * a) + (b * b))

-Tim

One way is to check an objects future position with the bounding box collision check Paul suggested. That is , if they try to move , find their future position and check it with the bounding box collision function. If there is a collision , then they can't move that direction so don't update their position. However , If an object moves more that it's width combined with another object's width , then it can skip over the object in front of it using this method.

Depending on what you want to do when a collision happens , if you just want to prevent the player from moving , then this would work fine.

However if you'd like to know which side it collided on , since it can only collide on the sides that it was moving towards , then check for overlaps in those directions.
Altering the previous code would give :

Your code for the collide_r function :

inline bool collide_r(int t1, int b1, int r1, int l1, int t2, int b2, int r2, int l2)
{
if (r1 == l2 && b1 > t2 && t1 < b2) return false;
else return true;
}

Semantically , that code is :
"If
(the right edge of object 1 is in the same place as the left edge of object 2) and (the bottom edge of object 1 is lower than the top edge of object 2) and
(the top edge of object 1 is higher than the bottom edge of object 2)
then no collision occurred , otherwise a collision occurred."

First of all , that will only work if you only ever move your objects by one at a time. Second , I think you've reversed the value that is returned by it. If all three of the conditions are true then a collision has occurred (The edges are at the same position and their dimensions perpendicular to the direction of movement overlap (collide_r is for when moving right , correct?)) but you return false.

Edgar Reynaldo: I have variables called walk_r, walk_l, walk_u and walk_d and if a collision occurred it turns to false and ex walk_r turns false.

OnlineCop: Thanks! I knew that I could made it esier but not that easy!

I've tried to use OnlineCops function but I getting errors This is my code:

if (collide_rect(image1, image2) == COLLISION_NONE)
{
walk_u = true;
walk_d = true;
walk_l = true;
walk_r = true;
}

And I get the error: invalid initialization of reference of type 'Objects&' from expression of type 'BITMAP*' in passing argument 1 of `int collide_rect(Objects&, Objects&)'

I don't understand the error but it's something with image1 and image2,
How should I do?

Oh yeah! Thanks man! I'll try this right away!

EDITED: OH!! Why won't it work! I've tried all ways but it just don't work!
I used your functions and came up to this:

And when I get in collision it just ignore it, I don't know how to do?
Please help me!

Mrukki, in the collision detection code you posted you have the checks as '=='. Ex: if(player1.left == player2.right) This wouldn't always work because player1's left could be past player2's right and still be having a collision.

594280
Try OnlineCop's code, it should work.

It should probably be something like:
if ((players[0] == &player2) && result != COLLISION_NONE))

The "players[0]" should be pointing to the address of player2, instead of to the object itself. See if that helps.

Semantically , there's nothing wrong with the line the way it was when you first got the error. From OnlineCop's code , players[0] and player2 are both 'Objects' objects. There may be some kind of include error. That's usually the only time I see the compiler suggest allegro's fixed class functions. You may have to actually write an equivalence operator for the Objects class(struct) yourself. I can't remember if the compiler supplies a default equivalence operator or not.

From http://www.cplusplus.com/doc/tutorial/classes.html :

So , no I don't believe the compiler supplies a default equivalence operator.

You could write one like this :

However , you could accomplish the same thing in OnlineCop's code by making players[2] an array of two pointers to player1 and player2 instead. You can only do that as long as the function parameters are Objects& (Objects references) though.
So you would use these kind of things instead :

That will only work if the character moves 1 pixel at a time. Do you remember to update the bottom right corner position values when the character moves?

In my previous post , if the code in the first window is too advanced for right now , the code in the second window was just a very minor modification to what you were using from OnlineCop's code. It was only to prevent the compiler error you were getting by allowing you to check if they were the same objects by checking to see if they had the same address in memory.