Sqlite3 adding custom function - c

Question

I'm trying to add a custom rank function written in C for SQLite3. The code compiles, but I can't seem to load it in sqlite3. When I do .load './librank.so' in SQLite3, I see this error message:
./librank.so.so: cannot open shared object file: No such file or directory
The code (from http://www.sqlite.org/fts3.html#appendix_a)
Rank.c
#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_RANK)
#include <stdio.h>
#ifndef SQLITE_CORE
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#else
#include "sqlite3.h"
#endif
static void rankfunc(sqlite3_context *pCtx, int nVal, sqlite3_value **apVal){
int *aMatchinfo; /* Return value of matchinfo() */
int nCol; /* Number of columns in the table */
int nPhrase; /* Number of phrases in the query */
int iPhrase; /* Current phrase */
double score = 0.0; /* Value to return */
assert( sizeof(int)==4 );
/* Check that the number of arguments passed to this function is correct.
** If not, jump to wrong_number_args. Set aMatchinfo to point to the array
** of unsigned integer values returned by FTS function matchinfo. Set
** nPhrase to contain the number of reportable phrases in the users full-text
** query, and nCol to the number of columns in the table.
*/
if( nVal<1 ) goto wrong_number_args;
aMatchinfo = (unsigned int *)sqlite3_value_blob(apVal[0]);
nPhrase = aMatchinfo[0];
nCol = aMatchinfo[1];
if( nVal!=(1+nCol) ) goto wrong_number_args;
/* Iterate through each phrase in the users query. */
for(iPhrase=0; iPhrase<nPhrase; iPhrase++){
int iCol; /* Current column */
/* Now iterate through each column in the users query. For each column,
** increment the relevancy score by:
**
** (<hit count> / <global hit count>) * <column weight>
**
** aPhraseinfo[] points to the start of the data for phrase iPhrase. So
** the hit count and global hit counts for each column are found in
** aPhraseinfo[iCol*3] and aPhraseinfo[iCol*3+1], respectively.
*/
int *aPhraseinfo = &aMatchinfo[2 + iPhrase*nCol*3];
for(iCol=0; iCol<nCol; iCol++){
int nHitCount = aPhraseinfo[3*iCol];
int nGlobalHitCount = aPhraseinfo[3*iCol+1];
double weight = sqlite3_value_double(apVal[iCol+1]);
if( nHitCount>0 ){
score += ((double)nHitCount / (double)nGlobalHitCount) * weight;
}
}
}
sqlite3_result_double(pCtx, score);
return;
/* Jump here if the wrong number of arguments are passed to this function */
wrong_number_args:
sqlite3_result_error(pCtx, "wrong number of arguments to function rank()", -1);
}
int sqlite3rankInit(sqlite3 *db){
sqlite3_create_function(db, "rank", -1, SQLITE_UTF8, 0, &rankfunc, 0, 0);
return 0;
}
#if !SQLITE_CORE
int sqlite3_extension_init(
sqlite3 *db,
char **pzErrMsg,
const sqlite3_api_routines *pApi
){
SQLITE_EXTENSION_INIT2(pApi)
return sqlite3rankInit(db);
}
#endif
#endif
Compiled with: gcc -shared -fPIC -lm rank.c -o librank.so
Can someone help me see what I did incorrectly?

Answer 1

Try to include the assert header
diff --git a/rank_orig.c b/rank.c
index 5d51b4d..4940e1b 100644
--- a/rank_orig.c
+++ b/rank.c
## -1,5 +1,6 ##
#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_RANK)
#include <stdio.h>
+#include <assert.h>
#ifndef SQLITE_CORE
#include "sqlite3ext.h"
Compile:
$ gcc -shared -fPIC -lm rank.c -o librank.so
Load
$ sqlite3
SQLite version 3.8.10.1 2015-05-09 12:14:55
sqlite> .load ./librank.so
sqlite>

Answer 2

The error message shows that SQLite already appends ".so" to the file name.
So you must specify the bare library name:
> .load './librank'