为什么我不能从字符串函数返回字符串数组？

Question

I would like to use my function to create a string array but my string function's return is not working.

string input() {
    int months[12] = { 31,28,31,30,31,30,31,31,30,31,30,31 };
    string array[12];

    for (int i = 0; i < 12; i++)
    {
        int j = 0;
        while (j < months[i])
        {
            array[i] = array[i] + "-";
            j++;
        }
            }
    return array[12];
}



int main() {

    string array[12];
    array[12] = input();
    return 0;
}

Answer 1

First of all your function is declared to return a single std::string object. Secondly, you return array[12] which is element thirteen of your twelve-element array.

And you can't actually return plain arrays from functions. Arrays decays to pointers to their first element, and that pointer would become invalid immediately as the life-time of the array ends when the function returns.

There are a couple of solutions: Either pass the array (as a pointer to the first element) as an argument to the function. Or return eg an std::array object.

Answer 2

array[12] is off the end of your array, and even if it were in bounds, it would be one string, not a collection of strings.

C style arrays are not assignable. std::vector<std::string> and std::array<std::string, 12> are alternatives that are assignable.

using MonthMarks = std::array<std::string, 12>;

MonthMarks input() {
    std::array<int, 12> months = { 31,28,31,30,31,30,31,31,30,31,30,31 };
    MonthMarks result;

    for (int i = 0; i < 12; i++)
    {
        int j = 0;
        while (j < months[i])
        {
            result[i] = result[i] + "-";
            j++;
        }
    }
    return result;
}

int main() {
    MonthMarks = input();
    return 0;
}

Note that std::string has a constructor that takes a size and a fill character, so your input can be simplified to

for (int i = 0; i < 12; i++)
{
    result[i] = std::string(months[i], '-');
}

Answer 3

Your problem is that your have the wrong syntax for what you're doing, and some of it isn't possible. Unfortunately, neither of that causes a compile time error, it just does something else, including undefined behavior.

You need to declare the function like this:

std::array<std::string, 12> input() {

You can't return an array, but if you wrap it into an std::array , you can.

Then do this inside:

std::array<std::string, 12> array;

And return it as

return array;

Get and print the data like this:

int main() {
    std::array<std::string, 12> array = input();
    for (std::string s : array) {
        std::cout << s << std::endl;
    }
    return 0;
}