迭代 std::vector 时的分段错误

我有一个连续多次调用的方法，用于对包含 std：：vectors 对象的 std：：vector 对象执行迭代打印。

class Message
{
public:
struct Child
{
Child:a(0.0F),b(0.0F)
{}
float a;
float b;
};
struct Parent
{
Parent:x(0U),y(0U)
{}
unsigned char x;
unsigned char y;
std::vector<Child> childList;
};
Message();
~Message();
printingMethod();
addParent();
private:
unsigned int s;
unsigned int t;
std::vector<Message::Parent> parentList;
}
Message::addParent(Message::Parent newParent)
{
parentList.push_back(newParent);
}
Message::printingMethod()
{
std::cout << s << std::endl;
std::cout << t << std::endl;
for(unsigned int i = 0U; i < parentList.size(); i++)
{
const Parent myParent = parentList[i];
std::cout << myParent.x << std::endl;
std::cout << myParent.y << std::endl;
for(unsigned int j = 0U; j < myParent.childList.size(); j++)
{
const Child mychild = myParent.childList[j];
std::cout << mychild.a << std::endl;
std::cout << mychild.b << std::endl;
}
}
}

Main()
{
Message myMessage;
//some code to initialise myMessage's vector by calling addParent
//....
//...
int idx = 0;
while (idx < 10000000)
{
myMessage.printingMethod();
idx++;
}
}

如果 while 循环只循环 100 次，就不会有问题。但是，如果我将 while 循环增加到 10000000 次，则本节将有可能出现分段错误：

for(unsigned int i = 0U; i < parentList.size(); i++)
{
const Parent myParent = parentList[i];//<-segmentation fault
std::cout << myParent.x << std::endl;
std::cout << myParent.y << std::endl;
for(unsigned int j = 0U; j < myParent.childList.size(); j++)
{
const Child mychild = myParent.childList[j];//<-segmentation fault
std::cout << mychild.a << std::endl;
std::cout << mychild.b << std::endl;
}
}

但是，如果我简单地将其更改为参考对象，则没有分割错误。

for(unsigned int i = 0U; i < parentList.size(); i++)
{
const Parent & myParent = parentList[i];//<-no segmentation fault
std::cout << myParent.x << std::endl;
std::cout << myParent.y << std::endl;
for(unsigned int j = 0U; j < myParent.childList.size(); j++)
{
const Child & mychild = myParent.childList[j];//<- no segmentation fault
std::cout << mychild.a << std::endl;
std::cout << mychild.b << std::endl;
}
}

谁能解释为什么我对复制的对象有分割错误，而不是对引用的对象？

还是"修复"只是侥幸，我最终会遇到分段错误？

蒂亚。