注意：'person::person()' 被隐式删除，因为默认定义的格式不正确

Question

我正在开发一个示例程序来帮助我学习 C++ 中的结构。这是我的代码：

#include <stdio.h>
#include <iostream>
#include <string>

using namespace std;

int nextPersonID = 0;
int nextAddressID = 0;

struct date {
    int day;
    int month;
    int year;
};

struct address {
    int id;
    string address;
    date effectiveDate;
    date expirationDate;
};

struct person {
    int id;
    string name;
    date birthdate;
    const int numberOfAddresses;
    address addresses [1];
};

int main () {
    person bob;
    bob.name = "Bob";
    bob.id = nextPersonID;
    nextPersonID++;
    bob.birthdate.day = 1;
    bob.birthdate.month = 1;
    bob.birthdate.year = 1990;
    bob.numberOfAddresses = 1;
    bob.addresses[0].address = "31415 E. Pi Blvd.";
    bob.addresses[0].id = nextAddressID;
    nextAddressID++;
    bob.addresses[0].effectiveDate.day = 1;
    bob.addresses[0].effectiveDate.month = 1;
    bob.addresses[0].effectiveDate.year = 1990;
    bob.addresses[0].expirationDate.day = 1;
    bob.addresses[0].expirationDate.day = 1;
    bob.addresses[0].expirationDate.day = 2020;
    cout << bob.name;
}

但是当我尝试编译时，它失败了 note: 'person::person()' is implicitly deleted because the default definition would be ill-formed.。这是我的构建日志：

-------------- Build: Debug in DataStructures (compiler: GNU GCC Compiler)---------------

mingw32-g++.exe -Wall -g -std=c++11 -I"C:\Program Files (x86)\CodeBlocks\MinGW_Dev_Libs\include\SDL2" -c C:\Users\Duncan\Documents\C++\Challenges\DataStructures\DataStructures.cpp -o obj\Debug\DataStructures.o
C:\Users\Duncan\Documents\C++\Challenges\DataStructures\DataStructures.cpp: In function 'int main()':
C:\Users\Duncan\Documents\C++\Challenges\DataStructures\DataStructures.cpp:32:12: error: use of deleted function 'person::person()'
C:\Users\Duncan\Documents\C++\Challenges\DataStructures\DataStructures.cpp:23:8: note: 'person::person()' is implicitly deleted because the default definition would be ill-formed:
C:\Users\Duncan\Documents\C++\Challenges\DataStructures\DataStructures.cpp:23:8: error: uninitialized non-static const member 'const int person::numberOfAddresses'
C:\Users\Duncan\Documents\C++\Challenges\DataStructures\DataStructures.cpp:39:29: error: assignment of read-only member 'person::numberOfAddresses'
Process terminated with status 1 (0 minute(s), 1 second(s))
3 error(s), 0 warning(s) (0 minute(s), 1 second(s))

我找不到任何与我的问题相关的 Google。有任何想法吗？ 我正在使用 Code::Blocks 和 g++。

Answer 1

好吧，问题不在于 "note"。 "note" 简单地解释了错误的原因。错误是当 class person 没有默认构造函数时，您试图默认构造 person 对象。

您可以 {}- 初始化该 const 成员，而不是尝试默认构造它，代码将编译

person bob = { nextPersonID++, "Bob", {}, 1 };
bob.birthdate.day = 1;
bob.birthdate.month = 1;
bob.birthdate.year = 1990;
...

或者，您可以简单地为 class.

编写您自己的默认构造函数

Answer 2

问题与default-constructor无关。 class 声明中有一个常量，但默认（无参数）构造函数不保证会定义该常量。建议使用“初始化列表”。

struct Person {
        int id;
        string name;
        date birthdate;
        const int numberOfAddresses;
        address addresses [1];
    
        Person(int); // constructor declaration
        Person() : numberOfAddresses(1) {} // constructor definition.
                      // ": numberOfAddresses(1)" is the initializer list
                      // ": numberOfAddresses(1) {}" is the function body
    };
    Person::Person(int x) : numberOfAddresses(x) {} // constructor definition. ": numberOfAddresses{x}" is the initializer list
    int main()
    {
        Person Bob; // calls Person::Person()
        Person Shurunkle(10); // calls Person::Person(int)
    }