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Type detection of enumerations #263

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dgl-cw opened this issue Aug 24, 2021 · 4 comments · May be fixed by #397
Open

Type detection of enumerations #263

dgl-cw opened this issue Aug 24, 2021 · 4 comments · May be fixed by #397
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@dgl-cw
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dgl-cw commented Aug 24, 2021

Automatic type detection on an enum fails, as the symbol_type returned by ADSIGRP_SYM_INFOBYNAMEEX (in adsGetSymbolInfo) is the name of the enum itself (e.g. E_something) instead of the underlying integer type.

Some testing showed that SAdsSymbolEntry.dataType i.e. the adsDataType of symbol matches the underlying type of the enum e.g. ADST_INT16 for INT and ADST_UINT16 for UINT.
I found this explanation why dataType is not used normally

pyads/pyads/symbol.py

Lines 176 to 179 in fd78232

# info.dataType is an integer mapping to a type in
# constants.ads_type_to_ctype.
# However, this type ignores whether the variable is really an array!
# So are not going to be using this and instead rely on the textual
But it could be used in addition to the symbol_type to detect unknown type names.
@stlehmann
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@dgl-cw thanks for bringing this up. Could you elaborate what the exact problem is that arises from this? E.g. will there be an error when reading/writing a value?

@dgl-cw
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dgl-cw commented Oct 20, 2021 •
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When trying to get the symbol, it misidentifies the type as String and procedes to raise an uncought UnicodeDecodeError when trying to decode that non-string. It's maybe just a get_symbol issue.

  File "main.py", line 64, in _get_symbol
    symbol = self.plc.get_symbol(name, *args, **kwargs)
  File "venv\lib\site-packages\pyads\ads.py", line 763, in get_symbol
    return AdsSymbol(self, name, index_group, index_offset, plc_datatype,
  File "venv\lib\site-packages\pyads\symbol.py", line 141, in __init__
    self._create_symbol_from_info()  # Perform remote lookup
  File "venv\lib\site-packages\pyads\symbol.py", line 166, in _create_symbol_from_info
    if info.comment:
  File "venv\lib\site-packages\pyads\structs.py", line 348, in comment
    return self._get_string(
  File "venv\lib\site-packages\pyads\structs.py", line 332, in _get_string
    return bytes(self.stringBuffer[offset:(offset + length)]) \
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xfc in position 2: invalid start byte

@stlehmann
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And the variable is declared as this?:

enum_var: ENUM_TYPE;

and you try to create a symbol like this?

sym = plc.get_symbol("GVL.enum_var")

@dgl-cw
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dgl-cw commented Oct 20, 2021

Yes, exactly.

@RobertoRoos RobertoRoos linked a pull request Jul 25, 2024 that will close this issue
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Added fallback to type detection to allow automatic ENUM usage RobertoRoos/pyads
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@stlehmann @dgl-cw