Continue while from nested for-loop

Question

I have the following loop structure:

while ($reader.Read() -eq $true)
{
    $row = @{}
    for ($i = 0; $i -lt $reader.FieldCount; $i++)
    {
        if(something...)
        {
            #continue with while
        }
    }
    #do more stuff...          
}

Now, is there any way to continue from within the for loop with the next iteration of the outer while loop without any break-variable? So if "something is true" I do not want to go #do more stuff but instead do the next $reader.read(). Continue only goes to the next iteration of the for loop. Break will only break the for loop.

Jeroen Mostert · Accepted Answer · 2014-10-16 15:31:44Z

13

Factoring out the inner loop to a function could improve readability, depending on how tangled up your variables are.

function processRow($reader) {
    $row = @{}
    for ($i = 0; $i -lt $reader.FieldCount; $i++)
    {
        if(-not something...) { return $null }
        # process row
    }
    $row
}

while ($reader.Read()) {
    $row = processRow $reader
    if ($row) {
        #do more stuff...          
    }
}

But if you want to do this directly, you can, because PowerShell has labeled breaks:

:nextRow while ($reader.Read()) {
    $row = @{}
    for ($i = 0; $i -lt $reader.FieldCount; $i++) {
        if(something...) {
            #continue with while
            continue nextRow
        }
    }
    #do more stuff...          
}

edited Oct 16, 2014 at 15:31

answered Oct 16, 2014 at 14:43

Jeroen Mostert

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6 Comments

silent Over a year ago

Thanks, those labled breaks seem to do the trick - though it feels somewhat like good old GOTO :)

Jeroen Mostert Over a year ago

Labeled breaks are what Donald Knuth would call a "structured GOTO" -- you cannot transfer execution to arbitrary places, only to well-defined ones (namely the ends of loops). To reinforce that, PowerShell doesn't even have a GOTO statement, which is fairly rare for a scripting language.

silent Over a year ago

Just a small edit: It's continue nextRow not break :nextRow

Jeroen Mostert Over a year ago

You're absolutely right -- break :nextRow will terminate the outer loop from inside the for, which is not what we want (in this case, but it's also useful).

silent Over a year ago

for me continue nextRow only works without the : With the : it will continue the for-loop

|

Raf · Accepted Answer · 2014-10-16 13:33:24Z

0

EDIT: a revised, recursive (and untested!) solution so your millage may vary:

function doReader()
{
    while ($reader.Read() -eq $true)
    {
        $row = @{}
        for ($i = 0; $i -lt $reader.FieldCount; $i++)
        {
            if(something...)
            {
                #continue with while
                doReader
                break;
            }
        }
    }
}
doReader
#do more stuff

edited Oct 16, 2014 at 13:33

answered Oct 16, 2014 at 11:30

Raf

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3 Comments

silent Over a year ago

Yeah, that's what I meant with "extra break-variable". I am currently using this but was looking for a nicer way ;)

Raf Over a year ago

@silent, give the edited answer a shot. Recursion is certainly more elegant

Jeroen Mostert Over a year ago

I wouldn't use recursion in a scripting language, because I wouldn't expect my future maintainer to understand it -- and I say this with all fondness for my future maintainers.

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