So I always seem to encounter this error. I usually find some odd hackish fix for it but this time I'm having too much trouble. I'm basically trying to make a program which corrects words the user types in (similar to that of any modern phone). The function I'm posting below is an attempt to make a vector of vectors. I am associating every letter with it's neighbor keys. For example...

If the user types in the letter 'A', I want a vector with the value 'A' to hold every letter that the 'A' key touches (Q, W, S, and Z). Every time I compile I get a subscript error. Any help would be appreciated.

vector< vector<string> > letterNeighbors; // VECTOR OF VECTORS

ifstream fin("iPhone_keyboard.txt"); // IPHONE KEYBOARD LIST
	char templateLetter; // FIRST LETTER
	string neighborLetter; // NEIGHBORING LETTERS

	getline(fin, neighborLetter); // GETS THE STRING OF CHARACTERS NEXT TO IT (NEIGHBORS)

	int neighborSize = neighborLetter.size(); // USED TO REFERENCE NUMBER OF ITERATIONS FOR LOOP
	int i = 0;

	while ( i < neighborSize )
	letterNeighbors.resize( 123, vector<string> (neighborSize) ); // RESIZES VECTOR
	letterNeighbors[templateLetter][i] = neighborLetter.substr(i);	// MAKES A VECTOR WITH THE TEMPLATE LETTER AND GRADUALLY ADDS NEIGHBORS


What's the error? Compile time or run time? If run time, have you tried putting in code to determine just which statement is causing the trouble?

Sorry, the error is in run time. I have tried resizing the vector multiple times. I get an error when the program tries to assign values...

letterNeighbors[templateLetter][i] = neighborLetter.substr(i);	// MAKES A VECTOR WITH THE TEMPLATE LETTER AND GRADUALLY ADDS NEIGHBORS

I only assign the number of values because of the error. The run time error persists even when the line where I resize the vector is removed.

Ok, so I have been messing around with the size of the vector and I decided to change the resize...

letterNeighbors.resize( 123, vector<string> (neighborSize) );


letterNeighbors.resize( 600, vector<string> (600) );

It works when I make the vector that large but it takes a longer time to run through the program. Any idea why it needs to be such a high number / how I can make it lower?

There is likely a default vector size, and 123 is smaller than the default, hence the error. Just a guess.

The default vector size is 0.

I knew that the default vector size was 0, I just thought that one of the reasons to use vectors was that they could resize themselves based on input. Even if a vector starts with a size of 0, when I add values it should automatically change it's size. Is that not correct? I would assume I could only get a "Subscript out of range" error if I specified the vector size and then tried to assign values outside of that range.

If v is a vector, v has undefined behavior if i is out of range (i.e. if i >= v.size()). Accessing v does not create that element (or any element) if that element does not already exist.

If you want to append a new element x to v, you can execute v.push_back(x), which will increase the size of v by one, and put a copy of x into the newly created element.

I guess I could solve the problem by including a push_back statement in the loop which would automatically add one value to the vector and then have it replaced immediately afterwards. Either way I am sticking with a resize I have found that works. It isn't the most efficient way but it works. Thanks.

I do not understand what you expect these two statements to accomplish:

letterNeighbors.resize( 123, vector<string> (neighborSize) );
letterNeighbors[templateLetter][i] = neighborLetter.substr(i);

After you have executed the first of these statements, letterNeighbors will have exactly 123 elements, each of which will be a vector. So when you execute the second statement, if the value of templateLetter is >= 123, the result will be a subscript out of range.