Diacritical folding in SQLite

Diacritical folding can be directly achieved in SQLite by implementing a custom function call. The following code demonstrates a possible implementation of such a function, taking in a string and returning a copy of the string with its diacritical marks folded.

#include <stdlib.h>
#include <sqlite3.h>
#include <stdio.h>
#include <CoreFoundation/CoreFoundation.h>

// this will be called by sqlite to dispose of the memory we malloced in diactrics_folding
void destruct_result(void * ptr)
{
    free(ptr);
}
void diactrics_folding(sqlite3_context* ctx,int cnt,sqlite3_value** val)
{
    char * in = (char *)sqlite3_value_text(*val);
    if(in == NULL)
        return;

    CFStringRef cstr = CFStringCreateWithCString(NULL, in, kCFStringEncodingUTF8);
    CFMutableStringRef str = CFStringCreateMutableCopy(NULL, 0, cstr);
    CFStringFold(str, kCFCompareDiacriticInsensitive, NULL);

    char * resultAsCString = malloc(strlen(in));
    if(!CFStringGetCString(str, resultAsCString, strlen(in), kCFStringEncodingUTF8))
    {
        free(resultAsCString);
        sqlite3_result_text(ctx, in, strlen(in), NULL);
        return;
    }
    sqlite3_result_text(ctx, resultAsCString, strlen(resultAsCString), &destruct_result);

    CFRelease(cstr);
    CFRelease(str);
}
int cback (void* udata,int ncol,char** value,char** colname)
{
    int i=0;
    for(;i<ncol;i++)
        printf("Result column: %s value: %s   \n", colname[i], value[i]);
    return 0;
}
int main()
{
    sqlite3 * handle;
    int res = sqlite3_open("./test.sql", &handle);

    res = sqlite3_create_function(handle, "diactrics_folding", 1, SQLITE_UTF8, NULL, &diactrics_folding, NULL, NULL);
 
    char * errmsg = NULL;   
    res = sqlite3_exec(handle, "select w, diactrics_folding(w) from t", &cback, NULL, &errmsg);
    printf("sqlite3_exec result: %d %s\n", res, errmsg != NULL ? errmsg : "No error");

    sqlite3_close(handle);
}

diciu$ gcc sqlite_diacritics.c -framework CoreFoundation -lsqlite3
diciu$ ./a.out
Result column: w value: mămăliguță cu brânză și smântână   
Result column: diactrics_folding(w) value: mamaliguta cu branza si smantana   
sqlite3_exec result: 0 No error