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lincsimp

stl iterator position

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Hi If I'm iteratind through a vector with this: for(iter = day_close.end();iter !=day_close.begin(); iter--) { } whats the best way to get the position it is in the vector? cheers

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Either keep track of it yourself, or rely on the fact that the vector's has fast array indexing, or that it's got a continous memory block by using pointer subtraction).
iter = vector.end();

for(size_t i = vector.size(); i; --i) {
// do stuff..
--iter;
}
Trying to process an element beyond the end of the vector first was intentional, right?

And if you're satisifed with a solution that only works with vectors and raw arrays then you might try this instead.

for(;;) {
size_t i = iter - vector.begin();
}

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C++ provides a function called std::distance for this very purpose.

Its in the <iterator> header file, and takes two iterators, you would pass in the begin() and current iterator.

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doynax brought up processing day_close.end(), which doesn't point to anything in day_close. That is almost certainly a bug. If you need to iterate through the list in reverse order you would use the reverse_iterator (it seems kinda of odd at first, but it make sense when you realise that you can use it in the stl alogorithms and what not).

For example

#include <iostream>
#include <vector>

using namespace std;

int main(int argc, char *argv[])
{
vector<int> test;
test.push_back(1);
test.push_back(2);
test.push_back(3);

vector<int>::reverse_iterator iter;
for(iter = test.rbegin();iter !=test.rend(); iter++){ //yes it's ++
cout << *iter;
}
cout << endl;

char junk;
cin.get(junk);
}





If you need to know the position, accessing the vector with operator[] instead of iterators maybe better suited for what your doing.

[Edited by - Cocalus on May 14, 2005 10:36:49 PM]

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