How to create a array/vector/matrix with number of dimensions unknown at declaration time.

[Jeff Alstott]

I'm having issues in a transformed data block with arrays and vectors whose size can only be determined after inspecting some of the data.

This code won't work, because two of the variables aren't defined at the beginning of the block:

int N_gap_updates;

N_gap_updates = sum(gap_lengths);

int gap_techs[N_gap_updates];

int gap_ts[N_gap_updates];

This code won't work, because the array variables will think N_gap_updates == 0:

int N_gap_updates;

N_gap_updates = sum(gap_lengths);

int gap_techs[N_gap_updates];

int gap_ts[N_gap_updates];

What to do?

[Daniel Lee]

We'll have compound define and declare soon, which wi solve the problem. For now, a little code duplication will work. 

int N_gap_updates;

int gap_techs[sum(gap_lengths)];

int gap_ts[sum(gap_lengths)];

N_gap_updates = sum(gap_lengths);

If you think that's gonna be massively wasteful, it isn't going to be a problem in practice. 

Daniel

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[Jeff Alstott]

That's what I thought the solution would be. The problem is that the minimal example I gave is actually not my main problem. I have a situation where merely calculating what the size of a vector should be is a dozen or more lines of code. Is the same solution still suggested?

[Daniel Lee]

Yes, but you shouldn't ever need to repeat dozens of lines of code. You can write a function for that. Or pass that as data from the outside. 

Daniel