No suitable conversion from "vector" to "vector"* exists?

Question

I am writing a program that will receive a text file, read in a list of names from that file, sort those names in alphabetical order, and then print the sorted list back out.

This originally was a project for my "Intro to Programming" class that was to use arrays, but I'm trying to retool it to work with vectors instead, allowing me to use a file of any length instead of a rigid array length.

But Intellisense is giving me an error:

No suitable conversion function from "std::vector<std::string, std::allocator<std::string>>" to "std::vector<std::string, std::allocator<std::string>>*" exists

Any time that I try to pass the filename to a function (ex at displayArray(names, nameQty), I get the error with names). I'm having a hard time googling how to pass a vector to a function, so I think that's where my problem is. The full code is pasted below:

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

int readFromFile(string[], string);
void displayArray(vector<string>[], int);
void alphaSort(vector<string>[], int);
void swap(string&, string&);


int main() {
//Declare variables
string fileName;
vector<string>names(1);
int nameQty;

//Prompt for file name
cout << "Please enter the name of the file to read names from: " << endl;
cin >> fileName;

//Call function to open file and read names into a vector array. Function will return the number of names in file
nameQty = readFromFile(names, fileName);

//Display unsorted names
cout << "Unsorted names:" << endl;
displayArray(names, nameQty);

//Sort names into alphabetical order
alphaSort(names, nameQty);

//Display sorted names
cout << "Sorted names:" << endl;
displayArray(names, nameQty);

//More to come after this; program isn't done yet!
}

/*
* Function to read a list from a text file into an array.
* The array starts at size 1, then increments by 1 for each subsequent iteration
* The array then deletes the final element when there is nothing more to read
* (since the last element will be uninitialized)
*/
int readFromFile(vector<string> array, string fileName) {

ifstream inputFile;
inputFile.open(fileName);

if (!inputFile) {
    cout << "Invalid file name. Please restart program and try again."
        << endl;
    system("pause");
    exit(EXIT_FAILURE);
}

else {
    int index = 0;
    while (inputFile) {
        cin >> array[index];
        array.push_back;
        index++;
    }
    array.pop_back;
    inputFile.close();
    return (index + 1);
}
}

//Function to display list of items in array
void displayArray(vector<string> array[], int quantity) {
    for (int i = 0; i < quantity; i++)
        cout << array[i] << endl;
}

//Selection sort function puts array elements in alphabetical order
void alphaSort(vector<string> names[], int qty) {
    for (int j = 0; j < qty - 1; j++) {

        for (int i = j + 1; i < qty; i++) {
            if (names[j] > names[i]) {
                swap(names[j], names[i]);
            }
    }
}

}

//Function to swap elements a and b in array
void swap(string &a, string &b) {
    string temp = a;
    a = b;
    b = temp;
}

Please don't worry about my using system("pause") and using namespace std. I'm aware that's poor practice, but it's what we've been asked to do in class.

Answer 1

You want:

void displayArray(vector<string>& array, int quantity)

or in this case even better:

void displayArray(const vector<string>& array, int quantity)

In your code it seems you are trying to pass an array of vectors (which is not that straightforward in C++ and boils down to a pointer to a vector in this case). To avoid copying you should use a reference.

You may also be interested to read about move semantics.

Also, as noted in the comments, you may also want to fix readFromFile:

int readFromFile(vector<string>& array, string fileName)

By changing it to a reference the function will modify caller's vector, instead of creating and modifying a local copy.