c++ - 无法在 C++ 中通过自动迭代映射

Question

我试图通过自动功能迭代这个简单的功能，但它给我带来了很多错误。我不知道这段代码有什么问题。

#include <vector>
#include <unordered_map>
#include <iostream>
using namespace std;

int main() {
  std::unordered_map<std::string, int> m = {
      {"apples", 5},
      {"bananas", 3},
      {"pears", 7},
  };
  for (auto& [fruit, count] : m) { //line 13
    std::cout << "I have " << count << " " << fruit << ".\n";
  }
}

13 [Error] expected unqualified-id before '[' token13

14 [Error] expected ';' before '[' token

13 [Error] 'fruit' was not declared in this scope

13 [Error] 'count' was not declared in this scope

还有更多的错误。我已经在线阅读了这个示例，它在那里运行良好。

Answer 1

Structured bindings是 C++17 的特性。

在 C++11 中迭代 std::unordered_map 看起来像这样:

for (auto const& p : m) {
    std::cout << "I have " << p.second << " " << p.first << ".\n";
}