Question

我不明白为什么第二个＆gt;父母一直向我显示2。矢量包含

{{2,4,0},{2,5,0},{2,6,0},{1,2,0},{8,7,0},{7,3,0},{10,9,0},{11,9,0},{3,9,0}, {1,3,0}, {0,1,11}}

在VS 2013上，我在Ideone它的工作中遇到了一个错误，但它一直看到我第二个＆gt; parent = 2.

struct tester {
    int parent, number, child;
};

std::vector <tester> test;
test.push_back({ 0,1, 11 });
std::vector <tester>::iterator first, second;

for (first = test.begin() + 1, second = test.begin(); first != test.end(); ++first) {

    if (first->parent <= second->parent) {
        parent = first->parent;

        auto pred = [parent](pracownik& item) {
            return item.parent == parent;
        };

        second = std::find_if(first - 1, test.begin(), pred);

        first->child = first - second;

        if (first->child == 1) first->child = 0;
        second = first;
    }

}

程序应将矢量更改为：

{ {2,4,0},{2,5,0},{2,6,0},{1,2,3},{8,7,0},{7,3,1},{10,9,0},{11,9,0},{3,9,2}, {1,3,5}, {0,1,11}}

Answer 1

std::find_if(InputIterator f, InputIterator l, UnaryPredicate pred)搜索范围[f, l)。在你的情况std::find_if(first - 1, test.begin(), pred);中，它应该是first - 1 <= test.begin()，但只有在for循环的第一次迭代时才会出现。

Find_if奇怪的值

1 个答案: