为什么2个NULL指针不能评估为false？

Question

我有一个相对简单的算法,它走std :: vector寻找两个相邻的元组.一旦找到X值左右两侧的元组,我就可以在它们之间进行插值.不知何故,这有效:

  std::vector<LutTuple*>::iterator tuple_it;
  LutTuple* left = NULL;
  LutTuple* right = NULL;
  bool found = 0;

  // Only iterate as long as the points are not found
  for(tuple_it = lut.begin(); (tuple_it != lut.end() && !found); tuple_it++) {
    // If the tuple is less than r2 we found the first element
    if((*tuple_it)->r < r) {
        left = *tuple_it;
    }
    if ((*tuple_it)->r > r) {
        right = *tuple_it;
    }
    if(left && right) {
        found = 1;
    }
  }

而这个:

  std::vector<LutTuple*>::iterator tuple_it;
  LutTuple* left = NULL;
  LutTuple* right = NULL;

  // Only iterate as long as the points are not found
  for(tuple_it = lut.begin(); tuple_it != lut.end() && !left && !right; tuple_it++) {
    // If the tuple is less than r2 we found the first element
    if((*tuple_it)->r < r) {
        left = *tuple_it;
    }
    if ((*tuple_it)->r > r) {
        right = *tuple_it;
    }
  }

才不是.这是为什么？我希望像这样的两个NULL pt在被否定时一起评估为true.

Answer 1

一找到第二个循环就会终止.将条件更改为:

tuple_it != lut.end() && !(left && right)

要么

tuple_it != lut.end() && (!left || !right)

继续,直到找到它们.