这是一个有效的例子.使用整数,需要调整浮点数.

#import <sqlite3.h>
static char *sepnum(int num,char *buf,size_t buflen,char sepch)
{
    int len = 0,negative = 0;
    if (!buf || buflen == 0) return buf;
    if (num < 0)
    {
        negative = 1;
        num = abs(num);
    }
    for (int i=1;;i++)
    {
        if (buflen>len+1) buf[len++] = '0' + (num % 10);
        num /= 10;
        if (num==0) break;
        if ((i % 3) == 0 && buflen>len+1) buf[len++] = sepch;
    }
    if (negative && buflen>len+1) buf[len++] = '-';
    for (int i=0;i<len/2;i++)
    {
        buf[len] = buf[i];
        buf[i] = buf[len-i-1];
        buf[len-i-1] = buf[len];
    }
    if (buflen>len) buf[len] = '\0';
    else buf[0] = '\0';
    return buf;
}
static void nformat(sqlite3_context *context,int argc,sqlite3_value **argv)
{
   if (argc == 1) 
    {
        int num = sqlite3_value_int(argv[0]);
        char buf[500] = "";
        if (sepnum(num,buf,sizeof(buf),','))
        {
            sqlite3_result_text(context,-1,sqlITE_TRANSIENT);
            return;
        }
   }
  sqlite3_result_null(context);
}

int main(int argc,char *argv[]) 
{
    sqlite3 *db;
    sqlite3_open(":memory:",&db);
    sqlite3_stmt *stmt;
    sqlite3_create_function(db,"nformat",1,sqlITE_UTF8,NULL,&nformat,NULL);
    sqlite3_prepare(db,"select nformat(1234)",&stmt,NULL);
    sqlite3_step(stmt);
    printf("[%s]\n",sqlite3_column_text(stmt,0));
}