int fieldDecimal(int fieldno);

The function fieldDecimal() returns a length of a fractinal part of a field by index.
It is suitable only for Numeric, Float, Double fields. For other types it returns 0.
It also returns 0 if index is out of range.

{
    // your code
    for (int i=0; i < dbf->fieldCount(); i++)
        printf( "%d\n", dbf->fieldDecimal( i ) );
    // your code
}