Store list of labels for input in C++ - c++

Question

I am getting error from cin >> theGift.m_wrap[i].m_pattern; part. I am new to C++. How do I store the patterns that the user enters? For example:
Enter wrapping pattern #1: Spots
Enter wrapping pattern #2: Stripes
Enter wrapping pattern #3: Zigzags
also, how would I access these?
struct Wrapping {
char m_pattern[MAX_WRAP];
};
struct Gift {
char m_description[MAX_DESC + 1];
double m_price;
int m_units;
int m_wrapLayers = 0;
Wrapping* m_wrap = new Wrapping[m_wrapLayers];
};
bool wrap(Gift& theGift){
if (theGift.m_wrapLayers == 0) {
cout << "Wrapping gifts..." << endl;
do {
cout << "Enter the number of wrapping layers for the Gift: ";
cin >> theGift.m_wrapLayers;
}while ((theGift.m_wrapLayers <= 0) && cout << "Layers at minimum must be 1, try again." << endl);
for (int i = 0; i < theGift.m_wrapLayers; i++) {
cout << "Enter wrapping pattern #" << i + 1 << ": ";
cin >> theGift.m_wrap[i].m_pattern;
}
return true;
}else {
cout << "Gift is already wrapped!" << endl;
return false;
}
}

Answer 1

Wrapping* m_wrap = new Wrapping[m_wrapLayers];
This line heap-allocates an array of zero elements because m_wrapLayers is zero at the moment this allocation happens. You never reallocate the array, so attempting to access any element of this array is undefined behavior since no elements exist.
You should be using std::vector which is a dynamically-sized container that does all of the following for you:
Makes a memory allocation to hold elements.
Reallocates when attempting to add an element to a full vector, copying over the old values.
Copies itself properly.
Deallocates memory when it's destroyed.
Right now you only do the first step, and you make an allocation that can't hold anything.
Vectors also know how many elements they hold, so you don't need to track that separately.
Additionally, you should use std::string instead of character arrays for strings. std::string is much like a vector of chars; it will grow as necessary.
I would redefine your types like this:
struct Wrapping {
std::string m_pattern;
};
struct Gift {
std::string m_description;
double m_price;
int m_units;
std::vector<Wrapping> m_wrap;
};
Then your code to populate the vector goes like this:
int layers;
do {
cout << "Enter the number of wrapping layers for the Gift: ";
} while ((!(cin >> layers) || layers <= 0) && cout << "Layers at minimum must be 1, try again." << endl);
for (int i = 0; i < layers; i++) {
cout << "Enter wrapping pattern #" << (i + 1) << ": ";
theGift.m_wrap.emplace_back();
cin >> theGift.m_wrap.back().m_pattern;
}