write once compile anywhere: mysqlclient
lazarus / 16-Databases

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hakelm · 2014-04-10 19:13

Using libmysqlclient I have written a program for querying a MySQL
database.
It compiles and runs without flaws under Linux i386 (Ubuntu) and
Windows xp, 7, 8.1. Under Ubuntu AMD-64 queries, however, truncates
fields and also returns empty fields.
Has anyone else seen this behaviour?
For the mysql-unit I use mysql.pp (Copyright (C) 2000 MySQL AB). I
have both tried cdecl and stdcall for the function prototypes but this
doesn't seem to matter.
My AMD-64 library is /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18
from 21/1 2014.
Any tip is appreciated.
H

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Mike.Cornflake · 2014-04-11 01:02

Both SQLDB and ZEOS provide working connections to MySQL.   I'm
presuming you're writing your own for a reason, however you could look
into their code, see how they do it...

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marcov · 2014-04-11 09:41

mysql protocol etc are highly versioned. Make sure your mysql unit is
prepared for 64-bit mysql and for the correct version.

Or use one of the supported versions that Mike named.

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LacaK · 2014-04-11 09:48

Quote from: hakelm on April 10, 2014, 09:13:03 pm
For the mysql-unit I use mysql.pp (Copyright (C) 2000 MySQL AB). I
have both tried cdecl and stdcall for the

From where do you use mysql.pp ? It is your own unit ?
(Can you try units (depends on version of your libmysqlclinet) from
packages/mysql/src ?)

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hakelm · 2014-04-13 19:33

No it's not my own unit, it can still be found on the internet and is
similar to mysql4.pp coming with Lazarus.
I have used it without problems for around 10 years.
I believe that I now have found the problem. The new libmysqlclient
for AMD-64 seems to have a bug in mysql_fetch_lengths which returns
erroneous values.
The code below doesn't work:
Code: [Select].............
row:=prow(mysql_fetch_row(fmysqlresult));
while row<>nil do
begin
fieldlengths:=plengths(mysql_fetch_lengths(fmysqlresult));
for x:=0 to fieldcount-1 do
begin
l:=fieldlengths^[x];
pf:=row^ [x];
s:=copy(pf,1,l);
result[x,y]:=s;
end;
inc(y);
row:=prow(mysql_fetch_row(fmysqlresult));
end;

But this seems to correct the problem:

Code: [Select]row:=prow(mysql_fetch_row(fmysqlresult));
while row<>nil do
begin
for x:=0 to fieldcount-1 do
begin
pf:=row^[x];
if pf<>nil then
result[x,y]:=pf
else
result[x,y]:='';
end;
inc(y);
row:=prow(mysql_fetch_row(fmysqlresult));
end;

H