具有多个指针初始化程序的C ++ for循环

Question

在下面的for循环中：

struct Block
{
    Block(int d) : data(d), next(nullptr) {}

    int data;
    Block* next;
};

Block* aList = new Block(1);
Block* bList = new Block(2);

for (Block* a = aList, *b = bList; a != nullptr; a = a->next, b = b->next)
    if (aList->data != bList->data)
        cout << "Difference found.\n";

我不喜欢将*放在b之前，但是当然需要将Block与Block *区分开。还有另一种方法吗？ for ((Block*) a, b...不适合。

Answer 1

您可以这样做：

for (auto a = aList, b = bList; a != nullptr; a = a->next, b = b->next)
    if (aList->data != bList->data)
        cout << "Difference found.\n";

Answer 2

如果您不想重复*，则可以使用using并创建一个别名BlockPtr，而不是Block*：

int main() {
  using BlockPtr = Block*;

  BlockPtr aList = new Block(1);
  BlockPtr bList = new Block(2);

  for (BlockPtr a = aList, b = bList; a != nullptr; a = a->next, b = b->next)
    if (aList->data != bList->data)
      cout << "Difference found.\n";
}

或在auto上中继：

int main() {

  auto aList = new Block(1);
  auto bList = new Block(2);

  for (auto a = aList, b = bList; a != nullptr; a = a->next, b = b->next)
    if (aList->data != bList->data)
      cout << "Difference found.\n";
}

Answer 3

是的，只需使用：

Block* a = aList, *b = bList

---

编辑：

选项1-使用Boost

#include <boost/typeof/typeof.hpp>
/*
    ...
*/
for (BOOST_TYPEOF_KEYWORD(Block*) a = aList, b = bList;...)

另一个选择是创建所需类型的单个变量，并使用该类型来初始化其他变量（类似于auto）：

选项2

Block* aList = new Block(1);
Block* bList = new Block(2);

for (decltype(aList) a = aList, b = bList; ...) ...

选项3-使用Boost

#include <boost/typeof/typeof.hpp>
/*
    Like the first option
*/
for (BOOST_TYPEOF(aList) a = aList, b = bList;...) ...
// ...

Answer 4

声明指针时，*属于名称，而不是类型。这意味着您可以使b这样的指针

for (Block *a = aList, *b = bList; a != nullptr; a = a->next, b = b->next)

Answer 5

您试图在一个表达式中声明两个指针。

Block* a = aList, b = bList;

它恰好是for循环的一部分，但是就像

int * a, * b;

是两个int指针，可以使用

Block* a = aList, * b = bList;

在您的for循环中。

Answer 6

仅定义type alias怎么样？

using BlockPtr = Block*;

for (BlockPtr a = aList, b = bList; a != nullptr; a = a->next, b = b->next)
    if (aList->data != bList->data)
        cout << "Difference found.\n";