C++ question


#1

I’ve got a relatively large array of maximal length LFSR masks I’d like
to be able to use, there are of course a different number for each
degree, increasing with the degree.

I forgot that C++ doesn’t support jagged arrays like C# so I created
this great little jagged array with the 2nd dimension 0 terminated (mask
of 0 isn’t really useful anyway, so I used it like null) so that I could
figure out how many were in each degree. I’ve been googling and IRCing
and trying to figure out if there’s a way to initialize a vector of
vectors as a constant in a class header file or something that would
hold these constants and coming up short on answers. Do I need to dump
all my data to a file and read it in? That seems poor for minimizing the
initialization delay. Is anyone willing to point me in the right
direction?


#2

Brett L. Trotter wrote:

I forgot that C++ doesn’t support jagged arrays like C# so I created
this great little jagged array with the 2nd dimension 0 terminated (mask
of 0 isn’t really useful anyway, so I used it like null) so that I could
figure out how many were in each degree. I’ve been googling and IRCing
and trying to figure out if there’s a way to initialize a vector of
vectors as a constant in a class header file or something that would
hold these constants and coming up short on answers. Do I need to dump
all my data to a file and read it in? That seems poor for minimizing the
initialization delay. Is anyone willing to point me in the right direction?

  1. You can initialize multidimensional c arrays at compile time:
    int a[2][2] = {{1, 2}, {3,4}};

  2. If I cared abound speed (like you do), I wouldn’t use vector of
    vector, rather a single long c-style array. (I’d use code to make it
    appear as it if is a 2-d array eventhough it’s 1-d.) And I’d use
    Stream.read and Stream.write to read/write it to disk which will be very
    fast. Using the example above:

int n = Rows * Cols;
int* a = new int[n];

// fill the array here using code

std::ofstream s(“array.bin”, std::ios::binary);
s.write(reinterpret_cast<const char*>(a), n * sizeof(int));

// subsequent loads will use the binary file:
std::ifstream s(“array.bin”, std::ios::binary);
s.read(reinterpret_cast<char*>(a), n * sizeof(int));

Chris