Remove Non-printable Characters From a String

Function/S RemoveNonPrintableChars_IP8(String inStr)
    // Store the bytes of the string in a byte wave so we can
    // use wave related commands.
    Variable len = strlen(inStr)
    Make/FREE/B/U/N=(len) byteWave
    byteWave = char2num(inStr[p])
   
    // Set all non-printable characters to 0 (null)
    // The test below considers tab (9), line feed (10), and carriage return (13)
    // to be printable characters.
    MultiThread byteWave = (byteWave[p] >= 32 && byteWave[p] <= 126) || (byteWave[p] == 9 || byteWave[p] == 10 || byteWave[p] == 13) ? byteWave[p] : 0
   
    // Extract the non-null values from the wave. These are the printable characters.
    Extract/O/FREE/B/U byteWave, printableByteWave, byteWave[p] > 0
   
    // Convert the wave's data back to a string.
    Variable np = numpnts(printableByteWave)
    String outStr = ""
    outStr = PadString(outStr, np, 0)
    Variable n
    For (n=0; n < np; n++)
        outStr[n,n] = num2char(printableByteWave[n])
    EndFor
    return outStr
End

#if IgorVersion() >= 9
Function/S RemoveNonPrintableChars_IP9(String inStr)
    // Store the bytes of the string in a byte wave so we can
    // use wave related commands.
    WAVE/B/U byteWave = StringToUnsignedByteWave(inStr)
   
    // Set all non-printable characters to 0 (null)
    // The test below considers tab (9), line feed (10), and carriage return (13)
    // to be printable characters.
    MultiThread byteWave = (byteWave[p] >= 32 && byteWave[p] <= 126) || (byteWave[p] == 9 || byteWave[p] == 10 || byteWave[p] == 13) ? byteWave[p] : 0
    WaveTransform zapZeros, byteWave        // Remove all of the nulls from the wave
    String outStr = WaveDataToString(byteWave)  // Convert the bytes in the wave back into a string.
    return outStr
End
#endif  // IP9+

Function/S RemoveNonPrintableChars(String inStr)
#if IgorVersion() >= 9
    return RemoveNonPrintableChars_IP9(inStr)   // MUCH faster
#else
    return RemoveNonPrintableChars_IP8(inStr)
#endif
End

Function testTime()
    Variable n
    Variable numTrials = 100
    Variable testStringLength = 1e5 // length of test string in bytes
   
    // Generate a test string that contains random bytes.
    String testString = ""
    testString = PadString(testString, testStringLength, 0)
    For (n=0; n < testStringLength; n++)
        testString[n,n] = num2char(trunc(abs(enoise(255))), 1)
    EndFor
   
    String outStr_IP8
    Variable aStart = StopMSTimer(-2)
    For (n=0; n < numTrials; n++)
        outStr_IP8 = RemoveNonPrintableChars_IP8(testString)
    EndFor
    Variable aStop = StopMSTimer(-2)
   
    Variable usingIP9OrLater = 0    // assume not using IP9 or later
#if IgorVersion() >= 9
    String outStr_IP9
    Variable bStart = StopMSTimer(-2)
    For (n=0; n < numTrials; n++)
        outStr_IP9 = RemoveNonPrintableChars_IP9(testString)
    EndFor
    Variable bStop = StopMSTimer(-2)
   
    // Make sure that the two methods give the same result.
    if (CmpStr(outStr_IP8, outStr_IP9, 2) == 0)
        print "The two methods give the exact same result."
    else
        print "WARNING: The two methods give different results."
    endif
   
    printf "RemoveNonPrintableChars_IP8: %g s   RemoveNonPrintableChars_IP9: %g s   %d trials.\r", (aStop-aStart)/1e6, (bStop-bStart)/1e6, numTrials
#else
    printf "RemoveNonPrintableChars_IP8: %g s %d trials.\r", (aStop-aStart)/1e6, numTrials
#endif
End

•testTime()
  The two methods give the exact same result.
  RemoveNonPrintableChars_IP8: 3.93585 s   RemoveNonPrintableChars_IP9: 0.207991 s   100 trials.