如何在成员初始值设定项列表中初始化数组

Question

Complete Beginner in C++.

This is a member initialization list:

Student.cpp

Student::Student(int studentID ,char studentName[40]) : id(studentID), name(studentName){};

Student.h

class Student{

protected:
    char name[40];
    int id;
}

My problem is that name is of type char[40] , so, name(studentName) displays an error of:

a value of type "char *" cannot be used to initialize an entity of type "char [40]"

How can I initialize name array, to studentName array in the member initializer list? I don't want to use string, and I have tried strcpy and didn't work

Answer 1

Since you can't initialize (raw) arrays with other arrays or even assign arrays in C++, you basically have two possibilities:

1. The idiomatic C++ way would be to use std::string , and the task becomes trivial:

    class Student{ public: Student(int studentID, const std::string& studentName) : id(studentID), name(studentName) {} protected: std::string name; int id; }; 

   Then, when needed, you can get the underlying raw char array from name by calling the c_str member function:

    const char* CStringName = name.c_str(); 

2. If you want to use a char array instead, things get more complicated. You can first default-initialize the array and fill it in the constructor body with strcpy :

    class Student{ public: Student(int studentID, const char* studentName) : id(studentID) { assert(strlen(studentName) < 40); // make sure the given string fits in the array strcpy(name, studentName); } protected: char name[40]; int id; }; 

   _{Note that the argument char* studentName is identical to char studentName[40] , since you can't pass arrays as parameters by value, which is why the compiler just treats it as a char* pointing to the first char in the array.}

Answer 2

You cannot implicitly copy arrays, they just do not have this feature. Here is what you can do instead:

The best option you have is safe the name in a std::string instead of an char[] . This would work just as your example, but could handle names of arbitrary length.

Another alternative would be std::array<char, 40> . This is nearly the same as the char[] you use right now, but has the advantage of being copyable. It also would work with the code you showed. Unlike the string option, this would be trivially copyable, ie you can for example send and receive this as binary data.

If you really want or need to use the char[] , you need to copy over the string "by hand":

Student::Student(int studentID ,char studentName[40]) : id(studentID){
    std::strcpy(name, studentName);
}