问题描述
这是我的代码
#include <iostream>
#include <vector>
#include <string>
using namespace std;
struct Student // EdgeContainer
{
string name = "";
vector<string> *addresses = nullptr;
Student()
{
cout << __FILE__ << " " << __LINE__ << " Student()" << endl;
}
Student(const Student &stu)
{
cout << __FILE__ << " " << __LINE__ << " Student(const Student &stu)" << endl;
name = stu.name;
addresses = stu.addresses;
}
void print()
{
cout << name << " " << addresses << " size=" << addresses->size() << endl;
if (addresses != nullptr)
{
for (int i = 0; i < addresses->size(); i++)
{
cout << i << " " << (*addresses)[i] << endl;
}
}
cout << "----------------\n";
}
};
struct Printer //ToyView
{
vector<Student *> students;
vector<vector<string>> stu_addresses;
void add_student()
{
for (int i = 0; i < 10; i++)
{
vector<string> address;
address.push_back("addr1");
address.push_back("addr2");
stu_addresses.push_back(address);
Student *stu = new Student;
students.push_back(stu);
students[i]->name = "stu" + to_string(i);
students[i]->addresses = &stu_addresses[i];
cout << i << " stu->address=" << stu->addresses << " size=" << stu->addresses->size() << endl;
}
}
void print()
{
cout << " students size=" << students.size() << endl;
for (int i = 0; i < students.size(); i++)
{
cout << i << " stu->address=" << students[i]->addresses << endl;
// students[i]->addresses = &stu_addresses[i];
students[i]->print();
}
}
};
int main()
{
Printer printer;
printer.add_student();
printer.print();
return 0;
}
这是一些结果:
../vector_cp.cpp 13 Student()
0 stu->address=0x563888ac6f30 size=2
../vector_cp.cpp 13 Student()
1 stu->address=0x563888ac7418 size=2
../vector_cp.cpp 13 Student()
2 stu->address=0x563888ac74f0 size=2
../vector_cp.cpp 13 Student()
3 stu->address=0x563888ac7508 size=2
../vector_cp.cpp 13 Student()
4 stu->address=0x563888ac76c0 size=2
../vector_cp.cpp 13 Student()
5 stu->address=0x563888ac76d8 size=2
../vector_cp.cpp 13 Student()
6 stu->address=0x563888ac76f0 size=2
../vector_cp.cpp 13 Student()
7 stu->address=0x563888ac7708 size=2
../vector_cp.cpp 13 Student()
8 stu->address=0x563888ac7a10 size=2
../vector_cp.cpp 13 Student()
9 stu->address=0x563888ac7a28 size=2
students size=10
0 stu->address=0x563888ac6f30
stu0 0x563888ac6f30 size=18446744073709549283
我希望students[0]->addresses.size() 应该是2,但它显示了垃圾数。 取消注释此行后 // student[i]->addresses = &stu_addresses[i]; 代码实际有效,即student[0]->addresses.size()。 我仍然无法弄清楚为什么会这样。有人可以帮忙吗?
解决方法
stu_addresses.push_back(address);
// ...
students[i]->addresses = &stu_addresses[i];
推回 stu_addresses
中的元素可能会重新分配您的向量,并且 stu_addresses
元素上先前有效的指针/迭代器将失效。
参见https://en.cppreference.com/w/cpp/container#Iterator_invalidation