Question

I created simple application, which uses sqlite3 as it’s datastore back-end. I faced no problems when building and running it on Linux, but after I tried to build it on Windows, I see weird linking error:

Linking dist\build\hnotes\hnotes.exe ...
C:\Documents and Settings\Admin\Application Data\cabal\sqlite-0.5.2.2\ghc-7.0.4/libHSsqlite-0.5.2.2.
a(sqlite3-local.o):sqlite3-local.c:(.text+0x21): undefined reference to `sqlite3_temp_directory'
C:\Documents and Settings\Admin\Application Data\cabal\sqlite-0.5.2.2\ghc-7.0.4/libHSsqlite-0.5.2.2.
a(sqlite3-local.o):sqlite3-local.c:(.text+0x40): undefined reference to `sqlite3_temp_directory'
collect2: v ld     1
cabal.EXE: Error: some packages failed to install:
hnotes-0.1 failed during the building phase. The exception was:
ExitFailure 1

What may be wrong there? I suspect that qalite3.dll has to be added to linking stage, but have no idea how to do that. Adding –extra-lib-dirs=path-to-sqlite-dll doesn’t help either (perhaps because I need to update my cabal file somehow, to support this?).

Answer 1

Not sure if It’s a bug or not, but the error comes from the sqlite3.h include of the sqlite package.

A look in the file shows this

/*
** CAPI3REF: Name Of The Folder Holding Temporary Files {H10310} <S20000>
**
** If this global variable is made to point to a string which is
** the name of a folder (a.k.a. directory), then all temporary files
** created by SQLite will be placed in that directory.  If this variable
** is a NULL pointer, then SQLite performs a search for an appropriate
** temporary file directory.
**
** It is not safe to modify this variable once a [database connection]
** has been opened.  It is intended that this variable be set once
** as part of process initialization and before any SQLite interface
** routines have been call and remain unchanged thereafter.
*/
SQLITE_EXTERN char *sqlite3_temp_directory;

so it’s declared as an extern. So simple test:

module Main where

import Database.SQLite

main 
 = do hwd <- openConnection "test"
      closeConnection hwd
      putStrLn "done"

This crashes during linking as expected with the error you have above.
So I created a small C test file foo.c

#include "sqlite-0.5.2.2\\include\\sqlite3-local.h"

char* sqlite3_temp_directory = "C:\\test2";

So I’m defining a temp_directory and then I pass the c file along during compilation of the haskell source

$ ghc test.hs foo.c
[1 of 1] Compiling Main             ( test.hs, test.o )
Linking test.exe ...

and then running it also returns the expected result

$ ./test
done

So it seems that you just need to give a value for the sqlite3_temp_directory, which if you set it to a NULL pointer will use the TMP/TEMP etc variables as defined in the SQLLITE manual.

edit, follow up on why it worked on Linux but not on windows

In the sqlite package, there’s a file sqlite3.c under the folder sqlite3.6. This provides a bunch of defaults for the sqlite package.

when on linux OS_UNIX is defined and when on linux it uses the defines under OS_WIN.
The function we’re interested in is the function which sets the temporary directory. for unix this’ll be unixGetTempname and for windows winGetTempname.

If you look at the implementation of both these functions, for the unix one it has list of directories that it’ll try

  static const char *azDirs[] = {
     0,
     "/var/tmp",
     "/usr/tmp",
     "/tmp",
     ".",
  };

it tries to access them in order and the one it can write to it uses to generate a temporary folder in.

For windows however one of the first lines are:

  if( sqlite3_temp_directory ){
    sqlite3_snprintf(MAX_PATH-30, zTempPath, "%s", sqlite3_temp_directory);
  }else if( isNT() ){

so for windows sqlite3_temp_directory is actually used. This is why it doesn’t compile if It can’t find it.