Iterator and Algorithm Patterns

Iterator Positions

Iterators can locate a value and turn that position back into an index for reporting.

iterator An iterator points at a position inside a container.
distance Subtracting random-access iterators reports how far apart two positions are.

Iterator Positions

target
iterator_positions.cpp
Replay: real traced execution (multi-file project)
#include <iostream>
#include <algorithm>
#include <vector>

int main() {
    std::vector<int> scores{72, 85, 91, 64};
    int target = 85;

    auto found = std::find(scores.begin(), scores.end(), target);
    int position = found == scores.end()
        ? -1
        : static_cast<int>(std::distance(scores.begin(), found));

    std::cout << "target=" << target << std::endl;
    std::cout << "position=" << position << std::endl;
    return 0;
}

#include <iostream>
#include <algorithm>
#include <vector>

int main() {
    std::vector<int> scores{72, 85, 91, 64};
    int target = 64;

    auto found = std::find(scores.begin(), scores.end(), target);
    int position = found == scores.end()
        ? -1
        : static_cast<int>(std::distance(scores.begin(), found));

    std::cout << "target=" << target << std::endl;
    std::cout << "position=" << position << std::endl;
    return 0;
}

#include <iostream>
#include <algorithm>
#include <vector>

int main() {
    std::vector<int> scores{72, 85, 91, 64};
    int target = 100;

    auto found = std::find(scores.begin(), scores.end(), target);
    int position = found == scores.end()
        ? -1
        : static_cast<int>(std::distance(scores.begin(), found));

    std::cout << "target=" << target << std::endl;
    std::cout << "position=" << position << std::endl;
    return 0;
}

  1. scores ← [72, 85, 91, 64], target ← 85, found ← (empty), position ← 1

    5int main() {6    std::vector<int> scores→ [72, 85, 91, 64]{72, 85, 91, 64};7    int target→ 85 = 85; //@target=64, 10089    auto found→ (empty) = std::find(scores[72, 85, 91, 64].begin(), scores.end(), target85);10    int position→ 1 = found(empty) == scores[72, 85, 91, 64].end()11        ? -112        : static_cast<int>(std::distance(scores[72, 85, 91, 64].begin(), found(empty)));1314    std::cout << "target=" << target85 << std::endl;15    std::cout << "position=" << position1 << std::endl;16    return 0;17}
    outputtarget=85
position=1

  1. scores ← [72, 85, 91, 64], target ← 64, found ← (empty), position ← 3

    5int main() {6    std::vector<int> scores→ [72, 85, 91, 64]{72, 85, 91, 64};7    int target→ 64 = 64;89    auto found→ (empty) = std::find(scores[72, 85, 91, 64].begin(), scores.end(), target64);10    int position→ 3 = found(empty) == scores[72, 85, 91, 64].end()11        ? -112        : static_cast<int>(std::distance(scores[72, 85, 91, 64].begin(), found(empty)));1314    std::cout << "target=" << target64 << std::endl;15    std::cout << "position=" << position3 << std::endl;16    return 0;17}
    outputtarget=64
position=3

  1. scores ← [72, 85, 91, 64], target ← 100, found ← (empty), position ← -1

    5int main() {6    std::vector<int> scores→ [72, 85, 91, 64]{72, 85, 91, 64};7    int target→ 100 = 100;89    auto found→ (empty) = std::find(scores[72, 85, 91, 64].begin(), scores.end(), target100);10    int position→ -1 = found(empty) == scores[72, 85, 91, 64].end()11        ? -112        : static_cast<int>(std::distance(scores[72, 85, 91, 64].begin(), found(empty)));1314    std::cout << "target=" << target100 << std::endl;15    std::cout << "position=" << position-1 << std::endl;16    return 0;17}
    outputtarget=100
position=-1