Returning Array in C++ returns unaccessable elements - c++

Question

I am working on a project where I parse a string in to an array and then return it back to the main function. It parses fine but when I return it to the main function I can't get access to the array elements.
//This is from the Main function. It calls commaSeparatedToArray which returns the array.
for (int i = 0; i < numberOfStudents; i++) {
string * parsedToArray = mainRoster->commaSeparatedToArray(studentData[i]);
Degree degreeType = SOFTWARE;
for (int i = 0; i < 3; i++) {
if (degreeTypeStrings[i] == parsedToArray[8])
degreeType = static_cast<Degree>(i);
}
mainRoster->add(parsedToArray[0], parsedToArray[1], parsedToArray[2], parsedToArray[3], stoi(parsedToArray[4]), stoi(parsedToArray[5]), stoi(parsedToArray[6]), stoi(parsedToArray[7]), degreeType);
}
//Here is the commaSeparatedToArray function
string * roster::commaSeparatedToArray(string rowToParse) {
int currentArraySize = 0;
const int expectedArraySize = 9;
string valueArray[expectedArraySize];
int commaIndex = 0;
string remainingString = rowToParse;
while (remainingString.find(",") != string::npos) {
currentArraySize++;
if (currentArraySize <= expectedArraySize) {
commaIndex = static_cast<int>(remainingString.find(","));
valueArray[currentArraySize - 1] = remainingString.substr(0, commaIndex);
remainingString = remainingString.substr(commaIndex + 1, remainingString.length());
}
else {
cerr << "INVALID RECORD. Record has more values then is allowed.\n";
exit(-1);
}
}
if (currentArraySize <= expectedArraySize) {
currentArraySize++;
commaIndex = static_cast<int>(remainingString.find(","));
valueArray[currentArraySize - 1] = remainingString.substr(0, commaIndex);
remainingString = remainingString.substr(commaIndex + 1, remainingString.length());
}
if (currentArraySize < valueArray->size()) {
cerr << "INVALID RECORD. Record has fewer values then is allowed.\n";
exit(-1);
}
return valueArray;
}

Answer 1

1) You can't return arrays in C++. Your code (as I'm sure you know) returns a pointer to an array. That's an important difference.
2) The array is declared locally in the function and therefore no longer exists after the function has exitted.
3) Therefore once you have returned from the function you have a pointer to something which no longer exists. Bad news.
4) You must always consider the lifetime of objects when you program C++. One solution to this problem is to dynamically allocate the array (using new[]). This means that the array will still exist when you exit the function. But it has the signifcant disavantage that you must remember to delete[] the array at a suitable later time.
5) The best solution (in general) is to use a std::vector. Unlike an array a std::vector can be returned from a function. So this option leads to the simplest, most natural code.
vector<string> roster::commaSeparatedToArray(string rowToParse) {
...
vector<string> valueArray(expectedArraySize);
...
return valueArray;
}
Since your array/vector is constant size, you could also use a std::array
array<string, expectedArraySize> valueArray;

Answer 2

To complete the answer that John has already given, I made some example code to show you, how such function could look like.
Parsing, or tokenizing can be easily done with the std::sregex_token_iterator. That is one of the purposes for this iterator. You can see the simplicity of the usage below.
In the function we define a vector af string and use its range constructor to do the whole tokenizing.
Then we make a sanity check and return the data.
Please see:
#include <string>
#include <regex>
#include <iterator>
#include <vector>
#include <algorithm>
#include <iostream>
const std::regex separator(",");
constexpr size_t ExpectedColumnSize = 9;
std::vector<std::string> commaSeparatedToArray(std::string rowToParse)
{
// Parse row into substrings
std::vector<std::string> columns{
std::sregex_token_iterator(rowToParse.begin(),rowToParse.end(),separator ,-1),
std::sregex_token_iterator() };
// Check number of columns
if (columns.size() != ExpectedColumnSize) {
std::cerr << "Error. Unexpected number of columns in record\n";
}
return columns;
}
// test code
int main()
{
// Define test data
std::string testInputData{ "1,2,3,4,5,6,7,8,9" };
// Get the result from the parser
std::vector<std::string> parsedElements{ commaSeparatedToArray(testInputData) };
// show the result on the console
std::copy(parsedElements.begin(), parsedElements.end(), std::ostream_iterator<std::string>(std::cout, "\n"));
return 0;
}