MATLAB: TEXTSCAN is the personal nemesis: Quotes strings with commas

loadreadstringstext filetextscan

Dear all,
I thought I acquired some Matlab knowledge over the years. But textscan really makes me feel dumb. I can not figure out the syntax to read a quoted text file.
Let's say I have a text file with the following format:
 "L1: quoted text, with commas","111.111",123\n
 "L2: quoted text, with commas","222.222",234\n
 ...
(the field width are the same just for the example; consider them variable in the real world).
Now my understanding of textscan's formatSpec would be:
format = '%q,"%f",%f';
delim  = '\n';
res = textscan(fileId,format,'Delimiter',delim,'ReturnOnError',false);
This is because I am assuming that %q considers everything between two quotes as part of the same string, as the help states
 "If the string begins with a double quotation mark ("), omit the leading quotation mark
  and its accompanying closing mark, which is the second instance of a lone double 
  quotation mark"
However this fails with the ominous error message:
 Error using textscan
 Mismatch between file and format string.
 Trouble reading 'Literal' field from file (row number 1, field number 2) ==>
 "L2: quoted text, with commas","222.222",234\n
So the commas in the quoted string somehow screw-up the parsing, since using the regexp-like
 format = '"%[^"]","%f",%f';
instead of %q works perfectly fine.
So my questions are:
  1. What am I doing wrong?
  2. Why is there the %q option if it does not treat everything in between as string (as this would than simply be a shorthand for "%s")?
  3. Am I using the delimiter option correctly?
Any help appreciated!
Greetings, David

Best Answer

fmt = '%q"%f"%f';
fid = fopen('temp5.txt','rt');
C = textscan(fid,fmt,'Delimiter',',');
fclose(fid);
Gives this:
>> C{:}
ans = 
    'L1: quoted text, with commas'
    'L2: quoted text, with commas'
ans =
  111.1110
  222.2220
ans =
   123
   234
And your questions:
  1. you are over-specifying the delimiter, and also confusing the delimiter with the end of line character |
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