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trapping Lua errors - nil and error
Trapping and handling errors. example from a Well House Consultants training course
More on Trapping and handling errors. [link]
Source code: splot Module: U111
--[[ Functions return 'nil' to indicate an error which you can trap. The error function lets you flag an error if you wish. ]] -- use io.write to supress new line io.write("please enter a number ... ") -- read from keyboard stuff = io.read() -- functions return nil if there's a problem value = tonumber(stuff) if value == nil then print "Nah!" else print ("That is half of ",value * 2) end print "code continues ..." -- flag an error if need be, and exit if value == nil then error("Wobbly thrown!") end print "code still continues ..." --[[ ------------ Sample Output ------------------ [trainee@easterton u111]$ lua splot please enter a number ... 42 That is half of 84 code continues ... code still continues ... [trainee@easterton u111]$ lua splot please enter a number ... forty two Nah! code continues ... lua: splot:26: Wobbly thrown! stack traceback: [C]: in function 'error' splot:26: in main chunk [C]: ? [trainee@easterton u111]$ ]] Learn about this subject
This module and example are covered on the following public courses:
* Learning to program in Lua * Lua Programming * Lua Programming Also available on on site courses for larger groups Books covering this topic
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This example comes from our "Trapping and handling errors." training module. You'll find a description of the topic and some
other closely related examples on the "Trapping and handling errors." module index page.
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