Declaring Variables in FoxPro (122907)

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Public Variables

Public variables, also known as global variables, are variables that may be used and modified by any FoxPro program and any of its sub-programs for the duration of the FoxPro session or until the variable is cleared from memory.

Public variables are declared in one of two ways:

1. Create a variable in the Command window. Any variable created in the Command window is automatically declared public. For example, from the Command window, type X=1000. The variable X is now public to all applications.
2. Within a program, declare a variable as public by using the PUBLIC command. In all programs, you must declare the variable as public before assigning it a value, as in this example code:

      PUBLIC var1
      var1=1000

Private Variables

Private variables are declared within programs or procedures and can be used and manipulated within that program or procedure and any of its sub-programs.

Private variables are declared one of three ways:

1. Create a variable inside a program or procedure without declaring is as public. The variable then becomes private to the program or procedure in which it is declared.
   
   For example, in the program MYPRG.PRG, declare var2 as private with this command:

         var2=2500
   						

   Now var2 is declared as private to MYPRG.PRG. It is available to all procedures called by MYPRG.PRG.
2. Include the variable on a PARAMETERS statement. This automatically causes the variable to become private to that program or procedure.
3. Use the PRIVATE command on variables declared previously. This makes the previously declared variable and its contents hidden. The new private variable becomes private to the current program or procedure. The PRIVATE command does not initially declare anything, a variable must already exist before PRIVATE can be used on it successfully.

Hidden Variables

Variables may not be declared hidden, but variables that were previously declared as Public or Private may become hidden. By hiding variables created in higher programs, you can enable variables of the same name to be manipulated in the current program without affecting the values of the hidden variables.

Once the program or procedure containing the private variables completes execution, all memory variables and arrays that were subsequently hidden are again available.

Variables are hidden in one of two ways:

1. If a variable has already been declared, use the PRIVATE command followed by the variable name to hide the existing variable and create a new PRIVATE variable.
2. Use a variable of the same name in a PARAMETERS statement. If a newly declared variable shares the same name as a variable previously declared, the previously declared variable becomes hidden and a new private variable is created for the current program or procedure.

To check the status of a variable, use the DISPLAY MEMORY command. DISPLAY MEMORY provides information about user-defined variables -- whether they are public, private, or hidden, and where (which program or procedure) they were declared.