problem with a loop, running infinitely

[nabh4u]

hi,
i have a program where every thing is working properly. i have a vector with some values. i use iterators and delete a specific value in the vector. here the loop runs infinitely only for some values. i dont know what is the problem.
sample code:

vector<int>::iterator Iterator;                    
for( Iterator = vect[temp3].cmatch.begin();     
        Iterator != vect[temp3].cmatch.end();Iterator++ )
{
    if(*Iterator==temp2)
    vect[temp3].cmatch.erase(Iterator);
}

here temp 2 and temp 3 are some temporary variables where i store some data temporaryily for each cycle. vect is a vector of the structure type i use and cmatch is just a vector of integer type.
i have some values in the cmatch which i compare with the value i want to delete and if equals i delete that value from the cmatch.
when i run this program and give all the input values it crashes and when i tried to debug it i found that this loop was going into infinite state.
i dont know what is the problem with this...
please help me as i have to submit my program within 2 days..
thank you in advance..

[RRick]

You have to be careful with erasing iterators. It is possible that the iterator is not valid after an erase.

To get around this problem, erase does return the value of the next valid iterator. Try this in your loop:

{
    if(*Iterator==temp2)
    Iterator = vect[temp3].cmatch.erase(Iterator);
}
 

[Banfa]

{
    if(*Iterator==temp2)
    Iterator = vect[temp3].cmatch.erase(Iterator);
}
 

Unfortunately this solution will cause the loop to not check values appearing after a value that is erased because of the ++ in the loop moving the iterator on 1 more. You need

vector<int>::iterator Iterator;                    
for( Iterator = vect[temp3].cmatch.begin();     
        Iterator != vect[temp3].cmatch.end(); )
{
    if(*Iterator==temp2)
    {
        Iterator = vect[temp3].cmatch.erase(Iterator);
    }
    else
    {
        Iterator++;
    }
}

[nabh4u]

Unfortunately this solution will cause the loop to not check values appearing after a value that is erased because of the ++ in the loop moving the iterator on 1 more. You need

vector<int>::iterator Iterator;                    
for( Iterator = vect[temp3].cmatch.begin();     
        Iterator != vect[temp3].cmatch.end(); )
{
    if(*Iterator==temp2)
    {
        Iterator = vect[temp3].cmatch.erase(Iterator);
    }
    else
    {
        Iterator++;
    }
}

hey first of all thank you for the suggestion..
i tried it..it works like the loop doesnt go into an infinite loop but when i display the values of the vector it does not delete the particular value...
for example: if i have only 2 values in d vector like 0 & 2 and when i do that loop 2 is equal and it should be deleted from the vector...bt it is not getting deleted. it is displayed in the output.
the output should be
0
but it shows
0 2
what should i do now??

[RRick]

Are you sure the erase method was called? The erase techinque in a loop is suppose to work. Try adding a cout after the erase to make sure.

There is another way to remove items from a vector and that is to use the erase-remove idiom (from "Effective STL" by Scott Meyers). This works well with vectors of ints and doubles. Try the following (I'm using Vector vect<int> as an example):

vect.erase( remove( vect.begin(), vect.enc(), 99));
 

[nabh4u]

Are you sure the erase method was called? The erase techinque in a loop is suppose to work. Try adding a cout after the erase to make sure.

There is another way to remove items from a vector and that is to use the erase-remove idiom (from "Effective STL" by Scott Meyers). This works well with vectors of ints and doubles. Try the following (I'm using Vector vect<int> as an example):

vect.erase( remove( vect.begin(), vect.enc(), 99));
 

thank you very very much...but i got the solution for my problem.
this works:

vector<int>::iterator Iterator;                    
for( Iterator = vect[temp3].cmatch.begin();     
        Iterator != vect[temp3].cmatch.end(); )
{
    if(*Iterator==temp2)
    {
        Iterator = vect[temp3].cmatch.erase(Iterator);
    }
    else
    {
        Iterator++;
    }
}