Return values

Like most standard library functions our functions should return ``0'' on success and a negative number (preferably ``-1'') on failure. Positve numbers are reserved for specific return values. Of course this rule is to be broken in many cases like:

• The return value is not of integer type.
  (If the return value is a pointer, NULL would be good to signal failure.)
• Negative numbers have to signal other stuff than error.
• etc.