Iterator algorithm: assignment

Weichao Wang

Dears,

Is it possible to assign an iterator to another one? With the following code I want to test it. But nothing will be printed except "vector filled".

#include <iostream>
#include <vector>
using namespace std;
int main(void) {
    vector<int> ivec;
    for (int i=0; i<10; ++i)
        ivec.push_back(i);
    cout << "vector filled" << endl;
    vector<int>::const_iterator iter;
    vector<int>::const_iterator itermemo;
    for (iter = ivec.begin(); iter != ivec.end(); ++iter) {
        if ((*iter) == 3) itermemo = iter;
        ++iter;
    }
    iter = itermemo;
    do {
        --iter;
        cout << *iter << endl;
    } while (iter != ivec.begin());
    //iter = itermemo;
    for (iter = itermemo; iter != ivec.end(); ++iter) {
        cout << *iter << endl;
        ++iter;
    }
    return 0;
}

Christian Ehrlicher

Because itermemo is not initialized at all and you don't check for iter != ivec.begin() before dereferencing the iterator in your second loop.
Why it's not initialized at all is a task for you, simply inspect the first loop.

/edit: same mistake in the third loop.

Weichao Wang

Dear Christian,

ivec contains 0 through 9, and with " if ((*iter) == 3) itermemo = iter;" itermemo must be initialized, if the syntax is correct. I expect the output 2 through 0 with the do loop and 3 through 9 in the last loop.

Christian Ehrlicher

@Weichao-Wang said in Iterator algorithm: assignment:

itermemo must be initialized,

No, please take a look on what you're doing with iter in your first and last loop.

Weichao Wang

@Weichao-Wang
Oh, I've found the problem. In the last two for loops I've repeated ++iter, which leads to the result that *iter == 3 would never be encountered. Thank you!

Weichao Wang

This post is deleted!

Christian Ehrlicher

@Weichao-Wang said in Iterator algorithm: assignment:

double instead of doppelt (which is German).

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