Is there a way in Matlab to determine the number of lines in a file without looping through each line?

Question

Obviously one could loop through a file using fgetl or similar function and increment a counter, but is there a way to determine the number of lines in a file without

Answer 1

I think a loop is in fact the best - all other options so far suggested either rely on external programs (need to error-check; need str2num; harder to debug / run cross-platform etc.) or read the whole file in one go. Loops aren't so bad. Here's my variant

function count = countLines(fname)
  fh = fopen(fname, 'rt');
  assert(fh ~= -1, 'Could not read: %s', fname);
  x = onCleanup(@() fclose(fh));
  count = 0;
  while ischar(fgetl(fh))
    count = count + 1;
  end
end

EDIT: Jonas rightly points out that the above loop is really slow. Here's a faster version.

function count = countLines(fname)
fh = fopen(fname, 'rt');
assert(fh ~= -1, 'Could not read: %s', fname);
x = onCleanup(@() fclose(fh));
count = 0;
while ~feof(fh)
    count = count + sum( fread( fh, 16384, 'char' ) == char(10) );
end
end

It's still not as fast as wc -l, but it's not a disaster either.