Backslash confusion

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  • freelance71
    #1

    Backslash confusion

    I have to pass the string '\abcd' to a function. Ofcourse one (or two) extra
    '\' is needed to escape but experimenting with it shows that I have to pass
    three extra backslashes to make it work.

    <script>
    var q = "\\\\abcd";
    displayLatex(q) ;
    </script>


    /* this function is in another file */

    function displayLatex(q) {


    alert(q); /* this shows \abcd when called by above script*/

    }


    Can anyone explain why this is so? why 4 backslashes?


    Tags: None
    • Erwin Moller
      #2
      Re: Backslash confusion

      freelance71 schreef:
      I have to pass the string '\abcd' to a function. Ofcourse one (or two) extra
      '\' is needed to escape but experimenting with it shows that I have to pass
      three extra backslashes to make it work.
      >
      <script>
      var q = "\\\\abcd";
      displayLatex(q) ;
      </script>
      >
      >
      /* this function is in another file */
      >
      function displayLatex(q) {
      >
      >
      alert(q); /* this shows \abcd when called by above script*/
      >
      }
      >
      >
      Can anyone explain why this is so? why 4 backslashes?
      >
      >
      I do not understand.
      Your script alerts \\abcd over here (on FF), as expected.
      There must be more to it than you describe.

      Regards,
      Erwin Moller

        Comment

        • freelance71
          #3
          Re: Backslash confusion


          "Erwin Moller"
          <Since_humans_r ead_this_I_am_s pammed_too_much @spamyourself.c omwrote in
          message news:4805abe9$0 $14343$e4fe514c @news.xs4all.nl ...
          freelance71 schreef:
          >I have to pass the string '\abcd' to a function. Ofcourse one (or two)
          >extra '\' is needed to escape but experimenting with it shows that I have
          >to pass three extra backslashes to make it work.
          >>
          ><script>
          >var q = "\\\\abcd";
          >displayLatex(q );
          ></script>
          >>
          >>
          >/* this function is in another file */
          >>
          >function displayLatex(q) {
          >>
          >>
          > alert(q); /* this shows \abcd when called by above script*/
          >>
          >}
          >>
          >>
          >Can anyone explain why this is so? why 4 backslashes?
          >
          I do not understand.
          Your script alerts \\abcd over here (on FF), as expected.
          There must be more to it than you describe.
          >
          Regards,
          Erwin Moller

          can it be because I'm using it in a PHP file like this?

          <?php

          echo <<< HTMLOUT

          <script>

          var q = '\\\\abcd';

          displayLatex(q) ;

          </script>

          HTMLOUT;

          ?>


            Comment

            • Erwin Moller
              #4
              Re: Backslash confusion

              freelance71 schreef:
              "Erwin Moller"
              <Since_humans_r ead_this_I_am_s pammed_too_much @spamyourself.c omwrote in
              message news:4805abe9$0 $14343$e4fe514c @news.xs4all.nl ...
              >freelance71 schreef:
              >>I have to pass the string '\abcd' to a function. Ofcourse one (or two)
              >>extra '\' is needed to escape but experimenting with it shows that I have
              >>to pass three extra backslashes to make it work.
              >>>
              >><script>
              >>var q = "\\\\abcd";
              >>displayLatex( q);
              >></script>
              >>>
              >>>
              >>/* this function is in another file */
              >>>
              >>function displayLatex(q) {
              >>>
              >>>
              >> alert(q); /* this shows \abcd when called by above script*/
              >>>
              >>}
              >>>
              >>>
              >>Can anyone explain why this is so? why 4 backslashes?
              >I do not understand.
              >Your script alerts \\abcd over here (on FF), as expected.
              >There must be more to it than you describe.
              >>
              >Regards,
              >Erwin Moller
              >
              >
              can it be because I'm using it in a PHP file like this?
              Yes. That is the reason.
              >
              <?php
              >
              echo <<< HTMLOUT
              >
              <script>
              >
              var q = '\\\\abcd';
              that becomes:
              var q = '\\abcd';

              in your HTML.
              Simply check your source in your browser to see it.

              Regards,
              Erwin Moller
              >
              displayLatex(q) ;
              >
              </script>
              >
              HTMLOUT;
              >
              ?>
              >
              >

                Comment

                • Thomas 'PointedEars' Lahn
                  #5
                  Re: Backslash confusion

                  freelance71 wrote:
                  >freelance71 schreef:
                  >>I have to pass the string '\abcd' to a function. Ofcourse one (or two)
                  >>extra '\' is needed to escape but experimenting with it shows that I have
                  >>to pass three extra backslashes to make it work.
                  [...]
                  can it be because I'm using it in a PHP file like this?
                  >
                  <?php
                  >
                  echo <<< HTMLOUT
                  >
                  <script>
                  >
                  var q = '\\\\abcd';
                  >
                  displayLatex(q) ;
                  >
                  </script>
                  >
                  HTMLOUT;
                  >
                  ?>
                  Yes, you have to escape each backslash for use with `echo'. A simple test
                  (with php -a) shows that

                  <?php

                  echo <<<HTML

                  var q = '\\a';

                  HTML;

                  ?>

                  displays only one backslash.

                  The simple and most efficient solution is to take heed of this general
                  advice: Do not let the PHP parser do things it does not have to.

                  <?php
                  ...
                  ?>
                  var q = '\\a';
                  <?php
                  ...
                  ?>

                  (The first and last part are optional, of course.)


                  F'up2 cl.php

                  PointedEars
                  --
                  realism: HTML 4.01 Strict
                  evangelism: XHTML 1.0 Strict
                  madness: XHTML 1.1 as application/xhtml+xml
                  -- Bjoern Hoehrmann

                    Comment

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