error C2512: no appropriate default constructor available (not classes)

问题

I'm starting out with structures, and I'm having problems dynamically allocating my structure array. I'm doing what I see in my book and on the internet, but I can't get it right.

Here's both full error messages:

C2512: 'Record' : no appropriate default constructor available

IntelliSense: no default constructor exists for class "Record"

#include <iostream>
#include <string>
using namespace std;

const int NG = 4; // number of scores

struct Record
{
    string name;  // student name
    int scores[NG];
    double average;

    // Calculate the average
    // when the scores are known
    Record(int s[], double a)
    {
        double sum = 0;

        for(int count = 0; count != NG; count++)
        {
            scores[count] = s[count];
            sum += scores[count];
        }

        average = a;
        average = sum / NG;
    }
};

int main()
{
    // Names of the class
    string names[] = {"Amy Adams", "Bob Barr", "Carla Carr",
                      "Dan Dobbs", "Elena Evans"};

    // exam scores according to each student
    int exams[][NG]= {  {98, 87, 93, 88},
                        {78, 86, 82, 91},
                        {66, 71, 85, 94},
                        {72, 63, 77, 69},
                        {91, 83, 76, 60}};

    Record *room = new Record[5];


    return 0;
}

回答1:

The error is quite clear. By the time you are trying to allocate an array:

Record *room = new Record[5];

a default constructor, i.e. Record::Record(), must be implemented so that 5 instances of Record can be created:

struct Record
{
    ...
    Record() : average(0.0) { }
    Record(int s[], double a) { ... }
};

Also note that dynamic allocation is something you want to avoid as much as possible in C++ (except the situations when you have really good reason for it). In this case it would be more reasonable to use an std::vector instead:

std::vector<Record> records(5);

来源：https://stackoverflow.com/questions/19850765/error-c2512-no-appropriate-default-constructor-available-not-classes

标签

c++

arrays

structure

dynamic-memory-allocation

dynamic-allocation