steve@tellab2.UUCP (Steve Harpster) (02/12/85)
Subject: Retrieving long relation returns bad character count
Index: ~ingres/source/libq/IIn_ret.c 4.2BSD
Description:
Occasionally, a C program (run through equel) which is trying to
retrieve tuples from an Ingres database returns the message
"IIn_ret: bad pb_get-1 <# bytes read>".
Repeat-By:
Create a relation with a character domain of length 255 (the
maximum). Now have a C program try and retrieve a tuple from it.
Fix:
Simple type conflicts. Casts fix the problem. The diffs are below:
*** /tmp/old_IIn_ret.c Tue Feb 12 13:22:31 1985
--- /user2/ingres/source/libq/IIn_ret.c Tue Feb 12 12:50:28 1985
***************
*** 46,53
ret = &IIr_sym;
if (ret->len &= 0377)
! if (IIpb_get(&IIpb, temp, ret->len & 0377) != ret->len & 0377)
! IIsyserr("IIn_ret: bad pb_get-1 %d", ret->len & 0377);
# ifdef xETR1
--- 46,54 -----
ret = &IIr_sym;
if (ret->len &= 0377)
! if ((length = IIpb_get(&IIpb, temp, ret->len & 0377)) != (int) (ret->len & 0377))
! IIsyserr("IIn_ret: bad pb_get-1, wanted %d got %d",
! (int) (ret->len & 0377), length);
# ifdef xETR1anton@ucbvax.ARPA (Jeff Anton) (02/14/85)
In article <220@tellab2.UUCP> steve@tellab3.UUCP (& Harpster) writes: > >Subject: Retrieving long relation returns bad character count >Index: ~ingres/source/libq/IIn_ret.c 4.2BSD > >Description: > Occasionally, a C program (run through equel) which is trying to > retrieve tuples from an Ingres database returns the message > "IIn_ret: bad pb_get-1 <# bytes read>". >Repeat-By: > Create a relation with a character domain of length 255 (the > maximum). Now have a C program try and retrieve a tuple from it. >Fix: > Simple type conflicts. Casts fix the problem. The diffs are below: > >*** /tmp/old_IIn_ret.c Tue Feb 12 13:22:31 1985 >--- /user2/ingres/source/libq/IIn_ret.c Tue Feb 12 12:50:28 1985 >*************** >*** 46,53 > ret = &IIr_sym; > > if (ret->len &= 0377) >! if (IIpb_get(&IIpb, temp, ret->len & 0377) != ret->len & 0377) >! IIsyserr("IIn_ret: bad pb_get-1 %d", ret->len & 0377); > > > # ifdef xETR1 > >--- 46,54 ----- > ret = &IIr_sym; > > if (ret->len &= 0377) >! if ((length = IIpb_get(&IIpb, temp, ret->len & 0377)) != (int) (ret->len & 0377)) >! IIsyserr("IIn_ret: bad pb_get-1, wanted %d got %d", >! (int) (ret->len & 0377), length); > > > # ifdef xETR1 The problem with the original code was not typeing but operator precidence. The '!=' would bind more causeing ret->len to be signextended to int and the comparison fails; then the result of the compairison is bit wise anded with 0377. There are many strange things about this code. For example, take the first if statement. 'if (ret->len &= 0377)' What is this supposed to do? ret->len is a char so &= with 0377 is a futile operation. Below is a much clearer version: if (ret->len != 0 && IIpb_get(&IIpb, temp, ret->len & I1MASK) != (ret->len & I1MASK)) IIsyserr("IIn_ret: bad pb_get-1, %d", ret->len & I1MASK); I1MASK is defined in h/ingres.h nontrivial question: Would casting ret->len as unsigned work better, not work, look better, or look worse? I know the answer. -- _________________________ C knows no bounds. Jeff Anton U.C.Berkeley ucbvax!anton anton@berkeley.ARPA