无法跳转到标签“fin”，错误：从这里开始，并经过初始化

Question

我最大的问题都在上面说了，无法跳转到标签fin（第27行错误），错误：从这里（第12和14行错误）和十字架初始化错误（第20行错误）请帮忙！

#include <iostream>
#include <string>

int main()
{
  std::string name;
  std::cout << "Please comply. y/n: ";
  std::string answer;
  std::cin >> answer;
  if (answer == "y"){std::cout << "You were spared." << std::endl; goto fin;}
  if (answer == "Miche"){std::cout << "The killers understood that you understood the prophecy, so they took you to their master" << std::endl; goto secret;}
  if (answer == "n"){std::cout << "You were brutally killed." << std::endl; goto fin;}
  else {std::cout << "You randomly babled " << answer << ", getting yourself killed."; goto fin;}
  secret:
  std::cout << "In order to fully find out if you are the legendary Miche, they took you to their leader."
  << " The master looked you over, and asked you one final question. The master asks you, fish?" << std::endl;

  std::string fish; fish = "none";
  std::cin >> fish;
  if (fish == "fish."){std::cout << "You were put in the throne of the king, where you ruled your near killers and their species for eternity."
  << std::endl; goto fin;}
  else {std::cout << "You failed and were immediately killed." << std::endl; goto fin;}
  goto fin;

  fin:

  return 0;
}

Answer 1

问题本质上是这样的：

int main() {
    if (whatever)
        goto fin;
    std::string fish;
fin:
    return 0;
}

如果whatever 为真，goto 会跳过fish 的构造。这是不允许的，因为编译器无法生成合理的代码来销毁fish，具体取决于是否执行了 goto。

解决方案：不要使用 goto。

可能性：

int main() {
    if (whatever)
        goto fin;
    {
    std::string fish;
    }
fin:
    return 0;

这里，fish 在块的末尾被销毁，因此 goto 不会引起问题（除了其固有的非结构化性质）。

更好：

int main() {
    if (!whatever) {
        std::string fish;
    }
    return 0;
}

Answer 2

您可以使用更简单的函数复制问题。

void foo()
{
   goto fin;
   std::string fish = "none";
   std::cin >> fish;

   fin:
}

为什么会有这样的问题？当执行跳转到fin:时，初始化fish的代码没有被执行。它的析构函数将在函数返回时被调用。由于将在未初始化的对象上调用析构函数，因此程序将表现出未定义的行为。

解决问题的最简单方法是将main 中的几乎所有内容放在另一个函数中，然后使用return 而不是goto。

void do_stuff()
{
   std::string name;
   std::cout << "Please comply. y/n: ";
   std::string answer;
   std::cin >> answer;

   if (answer == "y")
   {
      std::cout << "You were spared." << std::endl;
      return;
   }
   if (answer == "n")
   {
      std::cout << "You were brutally killed." << std::endl;
      return;
   }

   if (answer == "Miche")
   {
      std::cout << "The killers understood that you understood the prophecy, so they took you to their master" << std::endl;
   }
   else
   {
      std::cout << "You randomly babled " << answer << ", getting yourself killed.";
      return;
   }

   std::cout << "In order to fully find out if you are the legendary Miche, they took you to their leader."
      << " The master looked you over, and asked you one final question. The master asks you, fish?" << std::endl;

   std::string fish = "none";
   std::cin >> fish;
   if (fish == "fish")
   {
      std::cout << "You were put in the throne of the king, where you ruled your near killers and their species for eternity." << std::endl;
   }
   else
   {
      std::cout << "You failed and were immediately killed." << std::endl;
   }
}

int main()
{
   do_stuff();
}