ECPG: sizeof() in EXEC SQL DECLARE SECTION

Question

I have Sybase ASE CPRE Embedded SQL С code:

void MyFunc( MyClass*unit_address )
{
    EXEC SQL BEGIN DECLARE SECTION;
       CS_BINARY        var1[sizeof(MyClass)];
    EXEC SQL END DECLARE SECTION;
}

Try to migrate to PostgreSQL ECPG Embedded SQL С code:

void MyFunc( MyClass*unit_address )
{
    EXEC SQL BEGIN DECLARE SECTION;
       unsigned char      var1[sizeof(MyClass)];
    EXEC SQL END DECLARE SECTION;
}

But ecpg.exec pre-compiler returns:

d:\>"c:\Program Files\PostgreSQL\9.3\bin\ecpg.exe"-o 1.c 1.pgc
1.pgc: 4: ERROR: syntax error at or near  "("
error deleting output file "1.c" 

My solution:

void MyFunc( MyClass*unit_address )
{
    #define VAR1_SIZEOF sizeof(MyClass)
    EXEC SQL BEGIN DECLARE SECTION;
       unsigned char      var1[VAR1_SIZEOF];
    EXEC SQL END DECLARE SECTION;
    #undef VAR1_SIZEOF 
}

C code of function after pre-compile:

void MyFunc( MyClass*unit_address )
{
    #define VAR1_SIZEOF sizeof(MyClass)
    /* exec sql begin declare section */


#line 1 "1.pgc"
void MyFunc( MyClass*unit_address )
{
    #define VAR1_SIZEOF sizeof(MyClass)
    /* exec sql begin declare section */


#line 5 "1.pgc"
 unsigned char var1 [ VAR1_SIZEOF ] ;
/* exec sql end declare section */
#line 6 "1.pgc"

    #undef VAR1_SIZEOF 
}

but perhaps there is a more correct decision.