Double vector hides variables - c++

Question

I'm having an interesting problem when I'm accessing a double vector. The idea is that I have deleted all information prior to accessing the vector. A for loop tries to access the vector and successful says that the vector is empty, but when I access the vector point directly it shows that there are variables still in the vector.
Also, the vector was set up like so:
vector<vector<string>> proTable;
Here is the loop attempting to access the vector.
for(int a = 0; a < proTable.size(); a++)
{
for(int b = 0; b < proTable[a].size(); b++)
{
cout << proTable[a][b] << "\t";
}
}
But if I edit the for loop this way it returns the variable inside.
for(int a = 0; a < proTable.size(); a++)
{
for(int b = 0; b < proTable[a].size(); b++)
{
cout << proTable[a][b] << "\t";
}
cout << proTable[0][0];
}
The first prints nothing out. The second prints X which was in the vector before. Also, the vector does not show that it is empty.
This is how I was deleting it if it matters.
void MRelation::RemoveColumn(vector<int> rem)
{
while(!rem.empty())
{
int z = rem[rem.size() - 1];
for(int a = 0; a < proTable.size(); a++)
{
for(int b = z; b < proTable[a].size() - 1; b++)
{
proTable[a][b] = proTable[a][b+1];
}
proTable[a].pop_back();
}
rem.pop_back();
}
}
The vector rem holds the columns that need to be deleted from the table.

Answer 1

I have deleted all information prior to accessing the vector.
Accessing an vector out of bounds has undefined behaviour. Since your vector is empty, proTable[0] is out of bounds. In the line cout << proTable[0][0];, you access proTable[0]. Therefore the behaviour of your program is undefined.
it shows that there are variables still in the vector.
You cannot jump to such conclusion from observing undefined behaviour.
"There are variables still in the vector" was not necessarily the reason why you saw output. You saw output because the behaviour was undefined.

Answer 2

I found out what it was. I you delete the contents of the inner vector but don't delete the vectors themselves then the vector will think that it contains something still and will pull out information that doesn't exist anymore. here is the code I was have problems with. It has been edited with an if statement to correct it.
void MRelation::FinalPrint()
{
if(curTable.size() < 2)
{
ss << "? No\n";
}
else
{
ss << "? Yes(" << curTable.size() - 1 << ")\n";
}
if(!proTable[0].empty()) //This was added in after to correct the problem
{
for(int c = 1; c < proTable.size(); c++)
{
ss << " " << proTable[0][0] << "=" << proTable[c][0];
for(int d = 1; d < proTable[0].size(); d++)
{
ss << ", ";
ss << proTable[0][d] << "=" << proTable[c][d];
}
ss << "\n";
}
}
}
Sorry about not putting everything in context before. I was trying to put in as much relavant information without putting in 300 lines of code.