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add an example to setControlCHook #19416

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Jan 19, 2022
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add an example to setControlCHook #19416

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add an example to setControlCHook
Jan 19, 2022
adb425a
[skip CI] format example for setControlCHook
Jan 19, 2022
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9 changes: 9 additions & 0 deletions lib/system.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -2320,6 +2320,15 @@ when notJSnotNims:
proc setControlCHook*(hook: proc () {.noconv.})
## Allows you to override the behaviour of your application when CTRL+C
## is pressed. Only one such hook is supported.
## Example:
##
## .. code-block:: Nim
## proc ctrlc() {.noconv.} =
## echo "Ctrl+C fired!"
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this example is broken: ctrl-c hooks are signal handlers, and you can't (reliably) allocate memory inside them, which echo does - this is a common pitfall with using signal handlers

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I'm a new to Nim and I don't understand a lot, and when I wanted to catch Control-C I looked in system, and there was no example, but luckily I found one in stack overflow for Nim, otherwise I would have been stuck. It was suggested I make a PR to add the example, and this is the first PR I've make (and I had lots of hand-holding to do it from the Nim channel, to guide me step-by-step though the process), and so with that in mind, I'm confused...
I can do:

proc ctrlc() {.noconv.} =
  echo "Ctrl+C fired!"
  quit()

setControlCHook(ctrlc)

while true:
  discard

... and it does work?

## # do clean up stuff
## quit()
##
## setControlCHook(ctrlc)
Comment on lines +2323 to +2331
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For the future: runnableExamples are preferred for examples, since they're tested when the documentation is generated.

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Thank you - I was advised that in this case it would be tricky to send a ctrl-c for testing?

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@ringabout ringabout Jan 20, 2022 •
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You can use runnableExamples("-r:off"). But runnableExamples seems not to be able to be used for forward declare.

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Thank you once again xflywind. I don't know what "But runnableExamples seems not to be used for forward declare" means?

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It simply doesn't work for forward declare.

  proc setControlCHook*(hook: proc () {.noconv.})
    ## Allows you to override the behaviour of your application when CTRL+C
    ## is pressed. Only one such hook is supported.
    runnableExamples("-r:off"):
      proc ctrlc() {.noconv.} =
        echo "Ctrl+C fired!"
        # do clean up stuff
        quit()
      setControlCHook(ctrlc)

=> Error: invalid indentation


when not defined(noSignalHandler) and not defined(useNimRtl):
proc unsetControlCHook*()
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