c++ - 这段代码是如何工作的？

Question

我在看 C++ for dummies 并找到这段代码

#include <cstdio>
#include <cstdlib>
#include <iostream>
using namespace std;

int nextStudentId = 1000; // first legal Student ID
class StudentId
{
public:
StudentId()
{
    value = nextStudentId++;
    cout << "Take next student id " << value << endl;
}

// int constructor allows user to assign id
StudentId(int id)
{
    value = id;
    cout << "Assign student id " << value << endl;
}
protected:
int value;
};

class Student
{
public:
Student(const char* pName)
{
     cout << "constructing Student " << pName << endl;
     name = pName;
     semesterHours = 0;
     gpa = 0.0;
 }

protected:
string    name;
int       semesterHours;
float     gpa;
StudentId id;
};

int main(int argcs, char* pArgs[])
{
// create a couple of students
Student s1("Chester");
Student s2("Trude");

// wait until user is ready before terminating program
// to allow the user to see the program results
system("PAUSE");
return 0;
}

这是输出

Take next student id 1000

constructing Student Chester

Take next student id 1001

constructing Student Trude

Press any key to continue . . .

我真的很难理解为什么第一个学生 id 是 1000，如果 value 加一个然后打印出来

这有意义吗

在 studentId 的构造函数中，两行代码将 nextStudentId 加一，然后打印出来

输出会不会是这样的:

Take next student id 1001

constructing Student Chester

Take next student id 1002

constructing Student Trude

Press any key to continue . . .

希望你明白我想说的

谢谢

卢克

Answer 1

++ 是后自增运算符:它首先读取值(并将其分配给变量)，然后 增加它。

将此与 pre 增量运算符进行对比:

value = ++nextStudentId;

这将具有您期望的行为。

查看此问题以获取更多信息:Incrementing in C++ - When to use x++ or ++x?