SA0106: Virtual method calls in FB_INIT

Detects method calls in the FB_Init method of a base function block, which are overwritten by a function block derived from a base function block

Justification: In these cases, it could be that the variables in the overwritten methods are not initialized in the base FB.

Importance: High

Example 94. Example

The function block FB_A includes the methods FB_Init and Meth_MyInit. FB_Init calls Meth_MyInit for initialization. The function block FB_B is derived from FB_A. PLC_PRG calls FB_B and therefore uses its mbMyDintB variable before it has been initialized. FB_B.Meth_MyInit overwrites FB_A.Meth_MyInit.

FUNCTION_BLOCK FB_A
VAR
    mbMyDintA : DINT;
END_VAR

FUNCTION_BLOCK FB_B EXTENDS FB_A
VAR
    mbMyDintB : DINT;
END_VAR

METHOD FB_Init : BOOL
VAR_INPUT
    bInitRetains:BOOL;
    bInCopyCode:BOOL;
END_VAR
VAR
    diDummy:DINT;    //SA0106
END_VAR

mbMyDintA := 123;
diDummy := Meth_MyInit();

METHOD Meth_MyInit : DINT
VAR_INPUT
END_VAR

mbMyDintB := 123;    //access to member of FB_B

PROGRAM PLC_PRG
VAR
    g_BInst : FB_B;
    xVar : BOOL;
END_VAR

xVar := g_BInst.fb_init(TRUE, TRUE);
//this instruction causes the following order of initializations:
//FB_A.fb_init
//FB_B.Meth_MyInit    //SA0106
//FB_B.fb_init
//FB_B.Meth_MyInit

Output in the Messages view:

SA0106: Virtual method call 'Meth_MyInit' in FB_INIT