watch

Syntax

watch expression [if boolean-expression]

1. expression is a combination of variables, constants and operators.
2. boolean-expression is an optional boolean expression.

Usage

The watch command stops the program execution when the value of the expression changes.

If boolean-expression is provided, the watch command stops the execution of the program if the expression value has changed and the boolean-expression evaluates to true.

The watchpoint cannot be set if the program is not in the context where expression can be evaluated. Before using a watchpoint, you typically set a breakpoint in the function where the expression makes sense, then you run the program, and then you set the watchpoint. This example illustrates this procedure.

Example

MAIN
   DEFINE i INTEGER

   LET i = 1 
   DISPLAY i
   LET i = 2 
   DISPLAY i
   LET i = 3 
   DISPLAY i

 END MAIN

(fgldb) break main
breakpoint 1 at 0x00000000: file test.4gl, line 4
(fgldb) run
Breakpoint 1, main() at test.4gl:4
4      LET i = 1
(fgldb) watch i if i >= 3
Watchpoint 1:  i
(fgldb) continue
1
2
Watchpoint 1:  i

Old value = 2
New value = 3
main() at t.4gl:9
9         DISPLAY i
(fgldb)