A string or string expression containing the name of a variable
Returns .T. if variable exists, and .F. if it does not exist
Return true if a variable exists.
The eval_valid function used to test if a variable exists in Xbasic code, but was an expensive function to execute.
This is because it tested if an entire expression was valid,for example:
eval_valid("firstname + lastname")
In situations where there are a large number of calls to eval_valid(), the time taken by eval_valid() would become noticeable. As a result, the variable_exists() function was created specifically to test if a variable exists.
When the 'expression' tested by eval_valid() is simple (e.g. "Firstname"), then eval_valid() is functionally equivalent to variable_exists().
dim arr as p arr.foo.bar = "hello" ? variable_exists("arr.foo.bar") = .T. indx = 1 ? variable_exists("arr["+indx+"].foo.bar") = .T. ? variable_exists("arr[indx].foo.bar") = .T. indx = 2 ? variable_exists("arr["+indx+"].foo.bar") = .F. ? variable_exists("arr[indx].foo.bar") = .F. 'Forms can't be tested directly with this function, ' but there are two alternatives 'This form exists in AlphaSports p = form.load("customer information") ? Customer_Information.window_title = "Customer.dbf : Form View (Customer Information)" 'Variable_exists() cannot be used on certain Alpha Five desktop objects, ' such as forms ? variable_exists("Customer_Information.window_title") = .F. 'Note that eval_valid() for the same argument is .t. ? eval_valid("Customer_Information.window_title") = .T. 'On the other hand if we test p.window_title (since p is an ordinary xbasic variable), ' variable_exists() can be used ? variable_exists("p.window_title") = .T.