Question

我的代码在第20行崩溃，我尝试按用户输入的名称初始化名称。似乎矢量超出了范围。请帮我弄清楚背后的问题和原因。此代码从用户输入学生数据，根据成绩对其进行排序，然后将其打印回来。这是代码：

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

struct studentDatabase{
   std::string name;
   int grade;
};

void getUserInput(std::vector<struct studentDatabase> &student)
{
    std::cout << "No of students for which the data is to be entered n";
    int noOfStudents(0);
    std::cin >> noOfStudents;

    for (unsigned int i = 0; i < noOfStudents; ++i)
    {
       std::cout << "Enter name n";
       std::cin >> student.at(i).name;       // this is where it is crashing 
                                             //not sure why
       std::cout << "Enter grade n";
       std::cin >> student.at(i).grade;
   }
}

void sort(std::vector<struct studentDatabase> &student)
{
    for (unsigned int i = 0; i < student.size(); ++i)
    {
        for (unsigned int j = 0; j < student.size() -i; j++)
        {
           if (student.at(i).grade < student.at(j).grade)
               std::swap(student.at(i), student.at(j));
        }
    }
}

void printStudentOrder(const std::vector<struct studentDatabase> &student)
{
    for (unsigned int i = 0; i < student.size(); ++i)
       std::cout << student.at(i).name << " got a grade of " << 
       student.at(i).grade << std::endl;
}

int main() 
{
    std::vector<struct studentDatabase> student;
    getUserInput(student);
    sort(student);
    printStudentOrder(student);
    return 0;
}

Answer 1

std::vector<studentDatabase>最初是一个空容器。因此，当您通过vector访问vector::at(i)时，找不到任何项目，并且会引发out_of_range异常。

您可以先将数据收集到本地studentDatabase变量中，然后将其放入向量中，例如：

for (unsigned int i = 0; i < noOfStudents; ++i)
{
    studentDatabase s;
    std::cout << "Enter name n";
    std::cin >> s.name;

   std::cout << "Enter grade n";
   std::cin >> s.grade;
   student.push_back(s);
}

Answer 2

最初你的矢量是一个空容器。因此，当您尝试访问该向量时，它将引发异常。

void getUserInput(std::vector<struct studentDatabase> &student)
{
    std::cout << "No of students for which the data is to be entered n";
    int noOfStudents(0);
    std::cin >> noOfStudents;

    for (unsigned int i = 0; i < noOfStudents; ++i)
    {
       studentDatabase stud;
       std::cout << "Enter name n";
       std::cin >> student.name;       // this will get student name.

       std::cout << "Enter grade n";
       std::cin >> student.grade;     // this will get student grade.

       student.push_back(stud);   // Here we are storing the data into vector.
   }
}

您需要将数据存储到vecotor中以访问它们以避免异常。将此代码段替换为您的代码，您的问题将得到解决。

Answer 3

此时，您正在尝试访问位置i中的元素，但该向量最初为空。 vector构造的行为不像旧式数组，您必须在其中指定大小，并且所有这些空格都保留在内存中。

您必须创建您的矢量，其大小如此

std::vector<struct studentDatabase> student(30);
getUserInput(student);

但如果您之前不知道尺寸，我建议您逐个获取输入并使用push_back()

程序崩溃说矢量超出范围异常

3 个答案: