Add a function to determine the existence of a memory variable

Variables | functions
In the development application system, I used FoxPro On Error statement to write a function to judge the memory variable exist (), very convenient and practical, introduced to you here.
Design ideas: Assume that the memory variable exists, and then assign the memory variable to be judged to a temporary variable, and if the memory variable does not exist, the execution is bound to make an error, and an On Error statement will be executed when it goes wrong, as long as the memory variable exists in the function on error processing. In order not to affect the error handling of the caller, to ensure the versatility of the function, it is necessary to save and recover the possible error handling of the caller before and after function execution.
The source program is as follows:
existprg***
Para Memovari
Private Mexist,temp,olderror
Mexist=. T. assumes that memory variables exist
Olderror=on (′error′) to save the error handling of the calling program
On Error do Errhandle
temp= Memovari
On error Olderror to recover the calling program's fault handling
Retu Mexist return Presence flag
Proc Errhandle
Mexist=. F. Error is set to exist standard. F.