In user-exits, memory fields from the calling program are not available. With an external assign you can access any field of any calling program. This is also valid for field-exits, call functions, etc. You can even change the value of the field (at your own risk!)
DATA : zzname(30) VALUE '(SAPMV45A)VBAK-LIFSK'.
FIELD-SYMBOLS : < fs_lifsk&rt; TYPE ANY.
* Access main memory from program SAPMV45A field VBAK-LIFSK
ASSIGN (zzname) TO < fs_lifsk&rt;.
IF sy-subrc = 0.< br> IF < fs_lifsk&rt; = ...