Return Code Problems

Return code Problems caused by lack of proper Return code support in internal functions

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A major problem while

• searching for errors
• understanding the flow of the Library

is the lack of a meaningful return code when errors occur

• 1 : success
• 0 : failed
• -1 : general parameter error, otherwise not known

is, as a general rule, all that is returned.

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Due to the complexity of tasks being completed

• through checks are being done
  • but the true cause is not being stored or being reported

The time spent in searching for such errors

• is very high
  • so often I have build in errors codes
    • and i_rc variable with a default value of 0
    • each error determined (in the order found)
      • receives a minus value, starting with -1, -2 etc.
        • before the horrid goto error was called
      • or grouped according to some function typical logic
        • in the sample below, the groups are data-types
          • *_BIT, INT*, UINT* etc.
        • in combination with
          • RGB, GRAYSCALE, PALETTE, MULTIBAND etc.

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One sample in rl2tiff.c

• check_tiff_origin_pixel_conversion
  • this function determined an error
  • RL2_LoadRaster had failed with -1
    • 2-3 hours later, I found that the error was determined here
      • the cause of the error was elsewhere
  • there are about 25 different error possibilities
    • to resolve the problem, you must know which
  • In this case it was a 1_BIT, MONOCHROME, bitsPerSample error
    • with a value of 16604
      • bitsPerSample: default: 1 ; maximum: 8
        • so where does 16604 come from

So after about 5-6 hours

• the point where the error was determined is known

The cause of the problem was elsewhere

• init_tiff_origin
  • the LIBTIFF function TIFFGetField for retrieving TIFFTAG_BITSPERSAMPLE
    • was being used without checking the return code
      • in this case the GeoTiff had no field with TIFFTAG_BITSPERSAMPLE
        • in this case 1 should be set
      • due to the missing check, garbage was returned (16604)
      • this was the only case, where no checking was done
  • the LIBTIFF function TIFFGetFieldDefaulted
    • will return, when the GeoTiff has no TIFFTAG being queried
      • the predefined default value
        • not all TIFFTAG are supported
          • TIFFTAG_BITSPERSAMPLE is, however, supported

Resolvement:

• in cases where TIFFGetFieldDefaulted
  • will return (without a need to check the return code) a default value
    • TIFFGetField was replaced with TIFFGetFieldDefaulted
• otherwise
  • TIFFGetField with the checking of the return code is used

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It was after this full work day

• that I started to retained these return codes
  • up to then I had removed them
  • adding a switch/case
    • with a short description on what the code means

I would advice, that where needed

• that this system be continued

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[<-- 'Cutline / RasterDefaults Index'] (Cutline-Index#return_codes)

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2015-11-12: Mark Johnson, Berlin Germany

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