Help needed with an iterator going out of bounds

**jlanglopez** · 04-18-2009

I'm writing a program that simulates road traffic, I have a vector of integers inside a structure, which is itself the elements of a vector. Everything works fine except the iterator i use to delete elements of the inbedded integer vector seems to be going out bound and then when it trys to delete the element the program crashes.

The code that does this is here:

Code:

if (CAR_VEC[i].VELOCITY==0){ 
													vector<int>::iterator STEP;
													for (STEP=CAR_VEC[i].PASSD.begin(); STEP!=CAR_VEC[i].PASSD.end(); STEP++){
						
														if ( *STEP==ROAD_STOP[j]->NUM){
															cout <<"ok- bus:"<<i<<" pass:"<< *STEP<<" stop:"<<ROAD_STOP[j]->NUM<<endl;
															CAR_VEC[i].PASSD.erase(STEP); //something wrong with this line
															cout <<"erased"<<endl;}}

Where CAR_VEC is [vector < CARS > CAR_VEC;], cars being the struct which PASSD is inside.

The cout's are just so I can check that the integers I want are sensible, which they are. I've tried everything and nailed down the problem to something being deleted that isn't there. Yet I can't see why the iterator is going out of bounds. Is it something to do with the vector being inbedded in a structure, in which case do I need to declare the iterator as part of the larger vector CAR_VEC.

ie [ CAR_VEC[i].vector<int>::iterator STEP;] although I've tried this and it doesn't compile.

this is the output it gives

Code:

bus:21
2
2
2
0
0
0
2

ok- bus:21 pass:2 stop:2
erased
ok- bus:21 pass:2 stop:2
erased
ok- bus:21 pass:2 stop:2
erased
ok- bus:21 pass:2 stop:2

Passenger_vector has exited due to signal 11 (SIGSEGV).

Strangely it works fine as long as the number being deleted isn't the last one on the list.

**anon** · 04-18-2009

That's because erase invalidates the iterator and also makes the vector shorter, so if you increment the iterator blindly, you can well walk over the end of the vector.

Erasing from the container while iterating it is tricky but it looks basically like this:

Code:

for (iterator it = container.begin(); it != container.end; ) {
    if (condition) {
        it = container.erase(it);
    }
    else {
        ++it;
    }
}

Another, and probably better option, would be to create a function object and use the std::remove_if algorithm to do the dirty work.

Thread: Help needed with an iterator going out of bounds

Thread Tools

Search Thread

Display

Help needed with an iterator going out of bounds

Similar Threads

Going beyond bounds problem

Array bounds checking

out of bounds problem

C++ help needed

Game matrix bounds checking