如何编辑结构数组中的变量？

Question

I've Googled, asked my classmates, and finally asked my professor about this particular problem, but I haven't achieved a solution yet. I'm hoping someone here can help me out.

Basically, I need to make an array of structs that will contain 4 pieces of information per struct: country name, country population, country area, and country density. This information will be written to the structs in the array from a .txt document. This info will then be written onto the console from said array.

Unfortunately, in attempting to write anything to the structs in the array, I get 2 errors. "Cannot convert from 'const char[8]' to 'char [30]'" and "no operator '[]' matches these operands, operand types are: CountryStats [int]". These errors both refer to the line:

countries[0].countryName = "A";

Keep in mind that I have only started to use structs and this is the first time I've used them in an array. Also, I must use an array, as opposed to a vector.

Here's my code:

#include <iostream>
#include <fstream>
#include <string>
#include <vector>

struct CountryStats;
void initArray(CountryStats *countries);

const int MAXRECORDS = 100;
const int MAXNAMELENGTH = 30;

struct CountryStats
{
    char countryName[MAXNAMELENGTH];
    int population;
    int area;
    double density; 
};

// All code beneath this line has been giving me trouble. I need to easily edit the 
// struct variables and then read them.
int main(void)
{
    CountryStats countries[MAXRECORDS];
    initArray(*countries);
}

void initArray(CountryStats countries)
{
    countries[0].countryName = "A";
}

As of now I am just attempting to figure out how to write information to a struct within the array and then read the information off of it onto the console. Everything else should fall into place after I find the solution to this.

Oh, and one final note: I have not quite learned the function of pointers (*) yet. I am still relatively new to C++ as my past programming education has been primarily in Java. Any and all inclusions of pointers in this code have been influenced by my classmates and professor in the pursuit of solving this problem.

Thanks in advance!

Answer 1

You are not defining a definition for:

void initArray(CountryStats *countries);

but for:

void initArray(CountryStats countries);

in which countries is not an array. Since no operator[] is defined for CountryStats , the expression countries[0] fails to compile.

Since you cannot use std::vector (for some weird reasons), I'd suggest you to use an std::array :

template<std::size_t N>
void initArray(std::array<CountryStats, N>& ref) {
    for (std::size_t i = 0; i < N; i++)
        // initialize ref[i]
}

Of course, if you feel masochist, you can also use a C-style array:

void initArray(CountryStats* arr, int size) {
    for (int i = 0; i < size; i++)
        // initialize arr[i]
}

But you'll, probably, need to provide the dimension of the array as a second parameter.

Answer 2

Two problems

void initArray(CountryStats countries)

must be:

void initArray(CountryStats *countries)

And you must use strcpy to copy c style string. (but i suggest to use c++ string instead of char[])

strcpy(countries[0].countryName,"A");

But I say again, use c++ features like vector<> and string.