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Feature #1509

RingElems with empty input

Added by John Abbott over 3 years ago. Updated over 3 years ago.

Status:
Closed
Priority:
Normal
Assignee:
Anna Maria Bigatti
Category:
bug
Target version:
CoCoA-5.4.0
Start date:
14 Oct 2020
Due date:
% Done:

100%

Estimated time:
3.01 h
Spent time:
3.00 h

Description

In CoCoA-5 we have RingElems and RingElemList.
The second function can produce an empty list (from input "[]").
What should RingElems do when passed an empty string (or one full of whitespace)?

Currently it gives an unhelpful error mesg:

--> ERROR: Unexpected '\377'
--> [CoCoALib] ReadFactor
--> RingElems(R,"  ");
--> ^^^^^^^^^^^^^^^^^

Related issues

Related to CoCoALib - Design #1391: RingElems: syntax with [ and ] ?Closed2020-01-10

Related to CoCoALib - Design #1523: Input fns: action when when istream is in bad state?Closed2020-10-26

History

#1 Updated by John Abbott over 3 years ago

  • Related to Design #1391: RingElems: syntax with [ and ] ? added

#2 Updated by John Abbott over 3 years ago

  • Description updated (diff)

#3 Updated by Anna Maria Bigatti over 3 years ago

  • Description updated (diff)
  • Assignee set to Anna Maria Bigatti
  • % Done changed from 0 to 10
  • Estimated time set to 2.00 h

we want 

/**/  RingElems("     ");
[]

PS should also work for an empty string

Defined in RingElemInput.C

#4 Updated by John Abbott over 3 years ago

  • Description updated (diff)

#5 Updated by John Abbott over 3 years ago

  • Status changed from New to In Progress
  • % Done changed from 10 to 20

We could add the following at the start of RingElems (in RingElemInput:C:278)

    std::vector<RingElem> v;
    // Skip initial whitespace; if we hit EOF, return empty vector
    in >> std::ws;
    if (in.eof() || !in) return v;

I have just tried this, and it seems to work.

#6 Updated by Anna Maria Bigatti over 3 years ago

  • Tracker changed from Bug to Feature

Fixed in RingElemInput.C, therefore also for CoCoALib.

#7 Updated by John Abbott over 3 years ago

  • % Done changed from 20 to 50

Ah, me too. I have just checked in my code... oddly, there were no clashes. What does that mean?

#8 Updated by John Abbott over 3 years ago

  • Related to Design #1523: Input fns: action when when istream is in bad state? added

#9 Updated by John Abbott over 3 years ago

  • Status changed from In Progress to Resolved
  • % Done changed from 50 to 80

I have improved (??) the code. It should give better err mesgs now. Here are some examples:

/**/ RingElems(ZZ,",");
--> ERROR: Unexpected ','

/**/ RingElems(ZZ,"1,");
--> ERROR: Unexpected EOF

/**/ RingElems(ZZ,"*");
--> ERROR: Unexpected '*'

/**/ RingElems(ZZ,")");
--> ERROR: Unexpected ')'

/**/ RingElems(ZZ,"x");
--> ERROR: symbol not in ring
/**/

#10 Updated by Anna Maria Bigatti over 3 years ago

John Abbott wrote:

We could add the following at the start of RingElems (in RingElemInput:C:278)
if (in.eof() || !in) return v;

You are allowing (i.e. return empty vector) a problematic in. Why? Isn't this dangerous?

#11 Updated by John Abbott over 3 years ago

I do not think it is dangerous.

We cannot easily compare with C++ input via the >> operator since that reads into a variable which already has a value (and in the input stream is bad, the variable is left unchanged, I believe).

Note sure how relevant this is: C++ getline will return an empty string if applied to a stream which is bad (or already at EOF).

Since we offer a function test if a stream is at EOF (or bad?), we could simply make input operations from bad istreams into no-ops.
An alternative might be to throw exceptions, but exactly when? For the caller, it is probably simpler to check IsAtEOF before reading,
rather than having to put the read into a try...catch block.

#12 Updated by John Abbott over 3 years ago

  • Status changed from Resolved to Feedback
  • % Done changed from 80 to 90

I have also implemented RingElemVec (even though Anna did not want it).

I'll check in so we can test it.

#13 Updated by John Abbott over 3 years ago

Checked in.

#14 Updated by Anna Maria Bigatti over 3 years ago

  • Status changed from Feedback to Closed
  • % Done changed from 90 to 100
  • Estimated time changed from 2.00 h to 3.01 h

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