Technical Error message when given value is other than expected

Question

A computer program expects an input to be a certain value (lets say Value_A). Instead a different value is given (lets say Wrong_Value_B). My company is considering this sentence in such a situation:

"Value_A" was expected, when "Wrong_Value_B" given.

This seems to imply that "I expect A because you gave me B.", which is not correct as it suggests that if, for example, you gave me "C", I might expect some other value than "A".

Questions:

Is "when" appropriate? Does the sentence require a second "was" before "given"?

Possible Solutions:

I want to say "I need A and only A, no matter what. But you gave me B instead". I have suggested one of these alternatives:

• "A was expected, but B was given." or
• "B was given, when A was expected." or
• "A was expected, B given instead."

Answer 1

You may be confused because there are different meanings for when. Here's one that probably fits the use case you cite:

when adv
5. Whereas; although: She stopped short when she ought to have continued.
_{TFD Online}

So the meaning there is "A was expected, although B was given."

This corresponds pretty closely to your first suggested rewrite: "A was expected, but B was given."

Answer 2

I am not sure if this is really an English language question. Perhaps it would be more appropriate on software engineering.

Some points:

• we don't necessarily need to follow grammatically correct English for error messages, the important thing is that we are understood
• there could be thousands of errors generated by a program. In this sense it's often considered desirable to be concise, especially in a historical context when storage was more expensive.

I would tend to go with

Invalid input: "B"; expected: "A".

In this case we start by explaining the problem - there was an invalid input, then we explain what was expected.

I note that for example 30 years ago an MS-DOS computer would have given the message "bad command or file name", where bad is not really the best word here, but it is 'good enough' and is only three characters long. In my version of Windows that has been expanded to "'mdir' is not recognized as an internal or external command, operable program or batch file".

However if we type "dir /ss", then we still see the terse 'Parameter format not correct - "ss"'

This sentence is missing 'the' and 'is'.

Obviously my sentence is more specific in saying the problem 'invalid input', which is no longer than saying "was expected", and communicates the issue immediately.

If you wanted to be as verbose and specific and grammatically correct as possible, then you could go with something like "This function requires the input "A", however "B" was provided".

By the way the original question is a little ambiguous, but we might question the use of 'given'. We would tend to use the verbs 'provided' and 'passed', to refer to values given to functions. However from a style point of view in the context of computer errors I would tend to omit the verb entirely, as if we say 'invalid input', then the fact that we gave/provided/passed an input is already clear from the word input.

Answer 3

Is "when" appropriate?

"When" is correct, but it does lead to some ambiguity, as you've noted. As one commenter has remarked, "it could refer to a hypothetical (if) or be something concessive like although". Those possibilities are in addition to its most common meaning ("at that time").

Does the sentence require a second "was" before "given"?

Yes, the "rules" of English require a second "was" before "given" so that the finite clause has a finite verb. Sometimes it is possible to omit a repeated element (in this case, "was"), but I don't believe that most people would find that to be grammatical in this case.

I have suggested one of these alternatives:

I think that your first suggestion works very well: "A was expected, but B was given." The second option seems to repeat the ambiguity with "when", while the third contains a comma splice.