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keyboardgnuplotmousenumeric

How to fix this gnuplot error to handle key presses?

I'm trying to provide basic keyboard interaction for my gnuplot script. With gnuplot 5.4 patchlevel 1 I'm using MOUSE_CHAR as documented, I believe, however with the simplest script below, I get an error no matter what key I press.

while (1) {
    pause mouse keypress
    show variable MOUSE_

    if (exists("MOUSE_CHAR")) {
        if (MOUSE_CHAR == "w") {
            print "w"
        }
    }             # <-- line 114

    replot
}

The output shows the correct key pressed, for example:

        MOUSE_KEY = 119
        MOUSE_CHAR = "w"

or

        MOUSE_KEY = 114
        MOUSE_CHAR = "r"

But immediately after I get

"hrtp.gp" line 114: Non-numeric string found where a numeric expression was expected
Solution

  • The test for string equality is eq not ==, so you want if (MOUSE_CHAR eq "w") { print "w" }.