C++ vector erase crashes program

Question

My program creates projectiles that move forward, if they go out of certain bounds, they are to be deleted from the vector that they are stored in. The vector stores xcord, ycord, zcord, and their respective directions.

int size = bullet.size();
        for(int i = 0; i < size; i+=6)
        {
                float xc = bullet[i];
                float yc = bullet[i+1];
                float zc = bullet[i+2];
                float xd = bullet[i+3];
                float yd = bullet[i+4];
                float zd = bullet[i+5];
                if(xc > 100 || yc > 10 || zc > 100 || xc < -100 || yc < -10 || zc < -100)
                {
                      bullet.erase(bullet.begin()+i, bullet.begin()+i+5);
                      size=size-6;
                      i = i-6;
                }
                else
                {
                     glEnable(GL_TEXTURE_2D);
                     glBindTexture ( GL_TEXTURE_2D, texture_id[3] );
                     glPushMatrix(); 
                     glTranslatef( xc+(xd/2), yc+(yd/2), zc+(zd/2));   //x y z coord of sphere
                     glRotatef( 0,0,1,0);
                     glRotatef( -80,1,0,0); 
                     glRotatef( 0,0,0,1); 
                     glScalef( 0.10f, 0.10f, 0.10f); 
                     gluQuadricTexture(quadric,1);
                     gluSphere(quadric,10.0,72,72); 
                     glPopMatrix();
                     glDisable(GL_TEXTURE_2D);
                     bullet[i] = xc+xd;
                     bullet[i+1] = yc+yd;
                     bullet[i+2] = zc+zd;
                }
        }

But when a "bullet" goes out of bounds my program seems to crash. Any ideas?

Well changing

bullet.erase(bullet.begin()+i, bullet.begin()+i+5);

to

bullet.erase(bullet.begin()+i, bullet.begin()+i+6);

seems to have fixed it

For those interested

      bullet.push_back(xpos);
      bullet.push_back(0.0f);
      bullet.push_back(zpos);
      bullet.push_back(nxpos);
      bullet.push_back(nypos);
      bullet.push_back(nzpos);

happens whenever the mouse is clicked

It crashed whenever the sphere left the bounds, and was removed. I figure it was because I was trying to access a position in the vector that didn't exist — Adam Kenworthy, Mar 07 '13 at 11:39

score 5 · Answer 1 · answered Mar 07 '13 at 11:28

5

You have

i < size

as your condition, and accessing elements

bullet[i] .... bullet[i+5]

See anything wrong there? What happens when i reaches size-1. You'll access bullet[size + 4], right?

answered Mar 07 '13 at 11:28

Luchian Grigore

253,575
64
457
625

I changed the bullet.begin()+i+5) to bullet.begin()+i+6) and it appears to work. The vector can hold any number of projectiles, each of which take up 6 spaces – Adam Kenworthy Mar 07 '13 at 11:30
It won't happen as i is incremented by 6 each time – Tomer Arazy Mar 07 '13 at 11:31
@TomerArazy: Really? try walking through the code with size == 7 – PlasmaHH Mar 07 '13 at 11:33
@PlasmaHH - well, obviously in his code it's always that size%6 =0 – Tomer Arazy Mar 07 '13 at 11:34
@TomerArazy: How is that obvious? We never see how the code fills the bullets vector, and the OP says "The vector can hold any number of projectiles" – PlasmaHH Mar 07 '13 at 11:35
The moral of the story is - Use iterators, it's simpler – Adam Kenworthy Mar 07 '13 at 11:42
@AdamKenworthy No, the moral of the story is encapsulate your data. Use a `struct` at least, for `xc`, `yc`, `zc`, `xd`, `yd`, `zd`. – Peter Wood Mar 07 '13 at 12:02

score 3 · Answer 2 · answered Mar 07 '13 at 11:32

http://www.cplusplus.com/reference/vector/vector/erase/

Iterators specifying a range within the vector] to be removed: [first,last). i.e., the range includes all the elements between first and last, including the element pointed by first but not the one pointed by last.

The problem is that you're deleting only 5 elements instead of 6.

C++ vector erase crashes program

2 Answers2