alternatives to putting multiple placeholders

I have an 1000000*8 matrix which I am trying to output to a text file.

   fprintf(fid, '\n%12d %12d %12d %12d %12d %12d %12d %12d', P(:,1:8)')

If the matrix had more columns I would be writing the same placeholder (%12d) many more times. Is there a more efficient way to copy a large matrix to a text file preserving the rows and columns, possibly by writing the necessary placeholder just once.

Answer 1

[Walter Roberson]

No there is not.

You can, however, pre-calculate the format as a string and pass the string in to the call.

numcols = 8;
fmt = [ '\n', repmat('%12d ', 1, numcols) ];
fprintf(fid, fmt, P(:,1:8).');

Answer 2

[Jacob Halbrooks]

Since all of your data has the same format, you can let FPRINTF repeat the format specifier over all of your data. Here is an example of doing that:

data = rand(5,10);
for rInd = 1:size(data,1)
   fprintf('\n');
   fprintf('%12d ',data(rInd,:));
end

If your data is not regular enough for this, another approach would be to use REPMAT to dynamically create the format specifier for your data. I wrote an example of that here.