Re: Bidimensional vector with STL
On Thu, 05 Mar 2009 18:08:13 +0100, No_Name <no_mail@no_mail.com> wrote:
Hello,
I am trying to use the STL containers to create a bidimensional array.
In lots of websites, I found the following syntax that I use :
std::vector<std::vector<int>> vAcquired_Data;
For a test, I use the following code, and when I want to use this
vector as a bidimensional container, I get an "out of range error".
The code is as follows :
int x=0;
unsigned char *pData = new unsigned char[100];
Why not just:
unsigned char data[100];
Or if the non-constant nBytes is the size of the array:
vector<unsigned char> data(nBytes);
for (int i= 0; i < nbBytes -1; i += 2)
Do you really need to subtract 1 here?
{
vAcquired_Data[x][0] = pData[i];
vAcquired_Data[x++][1] = pData[i+1];
}
The error occurs at following line :
vAcquired_Data[x][0] = pData[i];
Can somebody help me here ? Thank you.
Vector items don't come into existence merely because you try to access
them. Your vector has no capacity at all, and you would need to do
something like this:
v.resize(50); // Create the row vectors
for (int i = 0; i < 50; ++i)
v[i].resize(2); // Size the rows
Or, you could omit this loop and use push_back inside your loop, e.g.
v[x].push_back(data[i]);
v[x].push_back(data[i+1]);
This is a matter of style, but I would tend to increment both loop
variables together, either at the end of the loop or in the third part of
the for-statement.
That said, vector-of-vectors isn't a great approach to 2D arrays. I prefer
the data to be stored densely, as it is for real 2D arrays. There may be
something to do this at boost.org.
--
Doug Harrison
Visual C++ MVP