Re: Wierdness using SUM to add results of custom C function.
От | Konrad Scherer |
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Тема | Re: Wierdness using SUM to add results of custom C function. |
Дата | |
Msg-id | 3C7A846C.CBF95D38@magma.ca обсуждение исходный текст |
Ответ на | Wierdness using SUM to add results of custom C function. (Konrad Scherer <kscherer@magma.ca>) |
Ответы |
Re: Wierdness using SUM to add results of custom C function.
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Список | pgsql-general |
Tom Lane wrote: > > Konrad Scherer <kscherer@magma.ca> writes: > > The C function returns the correct result all the time but the sum > > returns the wrong result all the time. It mostly returns 23, but it > > returned 24 once! > > Very strange. May we see the full text of the C function, and the > SQL declaration you gave for it? I was hoping someone would just say "Yeah I had that bug. Upgrade to .." ;-) Here is everything you need to reproduce this. C function #include "postgres.h" #include "executor/spi.h" int countwords(text *txt); //this function counts the number of commas in a comma seperated list //and then deduces the number of words in the list int countwords(text *txt) { int i, count; char * str; //retrieve string from text field str = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(txt))); //if no text, then no words if (txt->vl_len < 1) { return 0; } //if there is text, but no commas there must be one word count = 1; //ignore commas in first and last postion in list for (i=1;i<(txt->vl_len)-1;i++) { if (str[i]==',') { count++; } } return count; } An aside: should I be freeing str after I am done with it? It looks like it is only returning a pointer into the field. Compiled on Solaris using gcc -Wall -Wmissing-prototypes -Wmissing-declarations -fPIC -I/export/home/kscherer/postgresql-7.1.3/src/interfaces/libpq -I/export/home/kscherer/postgresql-7.1.3/src/include -c -o countWords.o countWords.c /usr/ccs/bin/ld -G -Bdynamic -o countWords.so countWords.o A quick script to run drop function countWords(text); CREATE FUNCTION countwords(text) RETURNS int AS '/export/home/kscherer/src/countWords.so' LANGUAGE 'C'; DROP table "sumtest"; CREATE table "sumtest" ( headwords text ); INSERT into sumtest values ( 'abattage/nm , abat/nm , abats/npl , abattis/npl , abattoir/nm , abatteuse/nf , abattant/nm , abat-son/nm , abat-foin/nm , abat-feuille/nm , abattable/adj , abat-voix/nm , abat-jour/nm , abatteur/nm , abat-vent/nm , abattu/adj , abattement/nm , s\'abattre/vp'); INSERT into sumtest values ( 'abate.vt, abate.vi, abatement.n'); INSERT into sumtest values ('abattoir/n'); select countwords(headwords) from sumtest; select sum(countwords(headwords)) from sumtest; Gives output (repeatedly) on my machine as follows countwords ------------ 18 3 1 (3 rows) sum ----- 23 (1 row) You can quickly verify that 18,3,1 are indeed the correct answers and that 23 is the worng one. It may have something to do with the parameter passing of the int in the C function, but then why does it work without using sum?? Thank You in advance Konrad Scherer
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