Question

我承认我完全被难过了。这是你只能从c ++这样的语言中获得的错误之一。

我有一个结构数组，我正在修改成员数据。真正的正常任务。我有一个函数可以获取一些成员数据，然后该函数调用另一个函数来获取其他成员数据。当我使用Visual Studio调试器逐步执行时，所有的分配似乎都很顺利。我在底部的调试窗口中观察变量的变化。但是一旦第二个函数返回到调用函数，数据就会消失。它可以追溯到未分配的乱码。任何想法？

编辑：不要将此问题标记为值/参考讨论的副本。它应该被删除以获得唯一性，或者单独留下。这个网站上的答案太多被标记为重复，因为其他地方的答案可能会回答问题，即使问题不同。如果问题不同，它们应该是分开的。

这两个功能：

void GetTestData(Student* students, int numStudents, int numTests)
{
  // Loop through the i students and all j tests
  for (int i = 0; i < numStudents; ++i)
  {
    // get test scores
    for (int j = 0; j < numTests; ++j)
    {
        cout << "What was " + students[i].Name + "'s score for test #" + to_string(j + 1) + "? ";
        cin >> students[i].Tests[j];
    }

    CalcGrades(students[i], numTests);
  }
}

void CalcGrades(Student student, int numTests)
{
  double sum = 0;

  // add up all the scores
  for (int i = 0; i < numTests; ++i)
  {
    sum += student.Tests[i];
  }

  // calculate the average and store it in the members
  student.Avg = sum / numTests;

  // grade assignment tree
  if (student.Avg >= 91)
  {
    student.Grade = 'A';
  }
  else if (student.Avg >= 81)
  {
    student.Grade = 'B';
  }
  else if (student.Avg >= 71)
  {
    student.Grade = 'C';
  }
  else if (student.Avg >= 61)
  {
    student.Grade = 'D';
  }
  else
  {
    student.Grade = 'F';
  }
}

Answer 1

@James Root所说的问题是通过引用传递vs传递值。对Student进行更改后，将其传递回数组。

Student* GetTestData(Student* students, int numStudents, int numTests)
{
  // Loop through the i students and all j tests
  for (int i = 0; i < numStudents; ++i)
  {
    // get test scores
    for (int j = 0; j < numTests; ++j)
    {
        cout << "What was " + students[i].Name + "'s score for test #" + to_string(j + 1) + "? ";
        cin >> students[i].Tests[j];
    }

    students[i] = CalcGrades(students[i], numTests); //after the value was changed, store it in the array
  }
  return students;
}

Student CalcGrades(Student student, int numTests)
{
  double sum = 0;

  // add up all the scores
  for (int i = 0; i < numTests; ++i)
  {
    sum += student.Tests[i];
  }

  // calculate the average and store it in the members
  student.Avg = sum / numTests;

  // grade assignment tree
  if (student.Avg >= 91)
  {
    student.Grade = 'A';
  }
  else if (student.Avg >= 81)
  {
    student.Grade = 'B';
  }
  else if (student.Avg >= 71)
  {
    student.Grade = 'C';
  }
  else if (student.Avg >= 61)
  {
    student.Grade = 'D';
  }
  else
  {
    student.Grade = 'F';
  }
  return student;
}

Answer 2

最好的解决方案是在GetTestData中将调用移到循环外的CalcGrades，并将其重写为所有学生的完整循环，就像其他函数一样。这避免了指针的缺点。

分配的数据未存储

2 个答案: