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POHow to remove trailing comments via regexp?
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copied!<p>For non-MATLAB-savvy readers: not sure what family they belong to, but the MATLAB regexes are described <a href="http://www.mathworks.nl/help/matlab/matlab_prog/regular-expressions.html" rel="noreferrer">here</a> in full detail. MATLAB's comment character is <code>%</code> (percent) and its string delimiter is <code>'</code> (apostrophe). A string delimiter inside a string is written as a double-apostophe (<code>'this is how you write "it''s" in a string.'</code>). To complicate matters more, the matrix transpose operators are <em>also</em> apostrophes (<code>A'</code> (Hermitian) or <code>A.'</code> (regular)). </p> <p>Now, for dark reasons (that I will <strong>not</strong> elaborate on :), I'm trying to interpret MATLAB code in MATLAB's own language. </p> <p>Currently I'm trying to remove all trailing comments in a cell-array of strings, each containing a line of MATLAB code. At first glance, this might seem simple: </p> <pre><code>>> str = 'simpleCommand(); % simple trailing comment'; >> regexprep(str, '%.*$', '') ans = simpleCommand(); </code></pre> <p>But of course, something like this might come along:</p> <pre><code>>> str = ' fprintf(''%d%*c%3.0f\n'', value, args{:}); % Let''s do this! '; >> regexprep(str, '%.*$', '') ans = fprintf(' %// <-- WRONG! </code></pre> <p>Obviously, we need to exclude all comment characters that reside inside strings from the match, while also taking into account that a single apostrophe (or a dot-aposrotphe) directly following a statement is an <em>operator</em>, not a string delimiter.</p> <p>Based on the assumption that the amount of string opening/closing characters <em>before</em> the comment character must be <em>even</em> (which I know is incomplete, because of the matrix-transpose operator), I conjured up the following dynamic regex to handle this sort of case: </p> <pre><code>>> str = { 'myFun( {''test'' ''%''}); % let''s ' 'sprintf(str, ''%*8.0f%*s%c%3d\n''); % it''s ' 'sprintf(str, ''%*8.0f%*s%c%3d\n''); % let''s ' 'sprintf(str, ''%*8.0f%*s%c%3d\n''); ' 'A = A.'';%tight trailing comment' }; >> >> C = regexprep(str, '(^.*)(?@mod(sum(\1==''''''''),2)==0;)(%.*$)', '$1') </code></pre> <p>However, </p> <pre><code>C = 'myFun( {'test' '%'}); ' %// sucess 'sprintf(str, '%*8.0f%*s%c%3d\n'); ' %// sucess 'sprintf(str, '%*8.0f%*s%c%3d\n'); ' %// sucess 'sprintf(str, '%*8.0f%*s%c' %// FAIL 'A = A.';' %// success (although I'm not sure why) </code></pre> <p>so I'm <em>almost</em> there, but not quite yet :) </p> <p>Unfortunately I've exhausted the amount of time I can spend thinking about this and need to continue with other things, so perhaps someone else who has more time is friendly enough to think about these questions: </p> <ol> <li>Are comment characters inside strings the <em>only</em> exception I need to look out for? </li> <li>What is the correct and/or more efficient way to do this? </li> </ol>

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