Test if a variable exists in Desktop

[turbojack]

I am trying to test to see if a simple global variable exists before creating a new one in xbasic. I was trying the variable_exist() and it works perfect if answer is true but if false get an error message. After doing more research found it is not for the desktop. Then tried eval() and eval_valid() with same results. If variable exists then it will give me answer of true but if it does not exist then get an error message.

I know I can do a work around by dim the variable in the autoexec. Is that the only way to solve my problem?

[Al Buchholz]

Re: Test if a variable exists in Desktop

From: http://wiki.alphasoftware.com/DIM

Note: A second DIM statement that redefines an existing variable does not cause an error. The value of the original variable is retained.
MyNote: If you use the = option of the DIM statement. Then the = doesn't work.

More specifically what are you trying to avoid and when are you doing this?

Note these results.

dim GLOBAL mytest as C
mytest="aa"
?eval_valid(mytest)
= .F.
?eval_valid(var->mytest)
= .F.
?eval_valid("var->mytest")
= .T.
?eval_valid("var->mytesta")
= .F.

?eval(mytest)
ERROR: Variable "aa" not found.
?eval(var->mytest)
ERROR: Variable "aa" not found.
?eval("mytest")
= "aa"
?eval("var->mytest")
= "aa"

[turbojack]

Re: Test if a variable exists in Desktop

Thanks. Learned something today. I was afraid if I dim a variable that already existed I would lose the value if the variable did exist. I have now played with this in the interactive window and see I can dim all day long and the variable if it exist will keep the value that it had.

Thanks for the quick answer Al.

[turbojack]

Re: Test if a variable exists in Desktop

I guess I was screwing up since I was not using the quotation marks (" ")

Dim GLOBAL mytest as c
?eval_valid("var->mytest")
= .T.
delete mytest
?eval_valid("var->mytest")
= .F.

delete mytest

[gkeramidas]

Re: Test if a variable exists in Desktop

if you don't care if the variable holds any data, just use:

delete mytest
dim global mytest as c

the delete {variable_name} does not pop an error if it doesn't exist. if it exists, it will delete it, if it doesn't exist, nothing happens.

[Al Buchholz]

Re: Test if a variable exists in Desktop

Be consistent with the scope of the variable.

http://wiki.alphasoftware.com/~alphafiv/DELETE

Delete needs to know the scope of the variable otherwise it assumes local.

[Stan Mathews]

Re: Test if a variable exists in Desktop

This may be a case where the interactive behaves differently.

dim mvar as C
dim shared myvar as N
dim global myvar as L
delete myvar

? a5_list_user_vars(local_variables())
= mvar
? a5_list_user_vars(session_variables())
= profile
? a5_list_user_vars(global_variables())
= myvar

[gkeramidas]

Re: Test if a variable exists in Desktop

Be consistent with the scope of the variable.

http://wiki.alphasoftware.com/~alphafiv/DELETE

Delete needs to know the scope of the variable otherwise it assumes local.

in my testing it doesn't seem to matter:

immediate window:

dim global mytest as n
dim global mytest as c
ERROR: Variable type mismatch: variable mytest is type 'N', attempted to assign type 'C'.

delete mytest

dim global mytest as c

[Al Buchholz]

Re: Test if a variable exists in Desktop

ran this script with debug - got this result.

image of script and debug

[gkeramidas]

Re: Test if a variable exists in Desktop

I guess that may be true if you dim the 3 types of variables with the same name. this is something I would never do. you could never be sure you're using the correct scope of the variable.

[Al Buchholz]

Re: Test if a variable exists in Desktop

I guess that may be true if you dim the 3 types of variables with the same name. this is something I would never do. you could never be sure you're using the correct scope of the variable.

Gary

The point is that the delete variable defaults to Local and needs to be specifically stated for Session or Global, otherwise you are deleting a Local variable not a Session or Global.

[gkeramidas]

Re: Test if a variable exists in Desktop

yes, it defaults to local, but if there is only a global variable with that name, a shared variable with that name or a local variable with that name, delete myvar will delete it without expressly telling it that it's a global , shared or local variable.

it deleted myvar because it's the only variable named myvar. in your example, with 3 different scopes, you have to explicitly tell it which one. when there is only one, delete myvar will delete any type of variable scope.

if you run this code it will show you the value of the character based variable and at the end, myvar will not be listed anywhere.

delete myvar ' doesn't even pop an error when a variable by this name does not exist
dim global myvar as n
myvar = 1
delete myvar
dim global myvar as c
myvar = "test global"
showvar(myvar)


delete myvar
dim shared myvar as n
myvar = 1
delete myvar
dim shared myvar as c
myvar = "test shared"
showvar(myvar)

delete myvar
dim myvar as n
myvar = 1
delete myvar
dim myvar as c
myvar = "test local"
showvar(myvar)

x=a5_list_user_vars(local_variables())
y=a5_list_user_vars(session_variables())
z =a5_list_user_vars(global_variables())

showvar(x + crlf() + y + crlf() + z)