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From:Miguel Cardenas Date:September 18 2005 5:25pm
Subject:mysql_free_result() CRASHES
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Hello

I've just experienced troubles with mysql_free_result() but don't know what is 
wrong... one of my programs has 2 simultaneous connections to MySQL and 
crashed when doing the mysql_free_result(), I thought it was 'cos the way I 
was making the program, but now I have the problem with single connection and 
still crashes randomly.

This is the part of of the source code, not to understand what does every 
function, just to illustrate, it is almost self-explanatory

--------------------------------------------------------
    MYCLASS dbmail;

   // CONNECT TO MYSQL
   if ( !dbmail.RealConnect(host,user,password) ) {
      printf("Unable to connect to %s...\n%s",host,dbmail.Error());
      return 0;
   }

   // SELECT DATABASE
   if ( dbmail.SelectDatabase((char*)DBM_DATABASE)!=0 ) {
      printf("Unable to open database: %s...\n",DBM_DATABASE);
      dbmail.Close();
      return 0;
   }

   // QUERY DATABASE
   // 'condition' is suplied by user ("where x=y", etc)
   sprintf(query_search,"SELECT address FROM DBM_ADDRESS %s",condition);
   if ( dbmail.RealQuery(query_search,strlen(query_search))!= 0 ||
        !dbmail.UseResult() ) { // leaves MYSQL_RES* stored inside the class
      printf("*** %s\n",dbmail.Error()); fflush(stdout);
      dbmail.Close();
      return 0;
   }

   MYSQL_ROW record;
   while ( (record=dbmail.FetchRow())!=NULL ) {
      printf("%s\n",record[0]);
   }
   //dbmail.FreeResult();

   dbmail.Close();
--------------------------------------------------------

When it reaches dbmail.FreeResult() it crashes... why? I don't know, by 
commenting that line everything works (although possibly resources are not 
free). The important member functions and internals involved in the code 
above are these: (handler, result arrays etc are inside the class)

--------------------------------------------------------
   class MYCLASS {
      ...
      private:
      MYSQL   sql_handle;
      MYSQL_RES  *sql_result;
      MYSQL_ROW  sql_rows;
      ...
   }

MYSQL_RES* MYCLASS::UseResult (void) {
   return (sql_result=mysql_use_result(&sql_handle));
}
MYSQL_RES* MYCLASS::StoreResult (void) {
   return (sql_result=mysql_store_result(&sql_handle));
}

MYSQL_ROW MYCLASS::FetchRow (void) {
   return mysql_fetch_row(sql_result);
}

void MYCLASS::FreeResult (MYSQL_RES* result) {
   if (result) {
      mysql_free_result(result);
   } else {
      mysql_free_result(sql_result);
   }
}
--------------------------------------------------------

In very short words, after the UseResult()/StoreResult()+FetchRows() when I 
call FreeResult() it crashes aleatory... MYCLASS members are very simple as 
you can see, it does not improve nothing new, just encapsulates a standalone 
connection with isolated pointers, arrays, etc.

What may be wrong that when mysql_free_result(sql_result); is called the 
program crashes? NOTE THAT ALL DATA IS RETRIEVED SUCCESSFULLY AND COMPLETE, 
THE PROBLEM COMES WHEN I FREE THE RESOURCES...

*** glibc detected *** double free or corruption (!prev): 0x08051d58 ***
Aborted

mysql_free_result(sql_result) is called ONLY ONE TIME, so why the hell the 
error says double free? that reduces options to corruption but why?

I will try to move to an older MySQL (currently have the latest) to see if the 
error continues, but if it persists, what may produce the error? the way 
I ./configure'd it maybe?

Thanks for your patience...

Thread
mysql_free_result() & 2 different connectionsMiguel Cardenas17 Sep
  • Re: mysql_free_result() & 2 different connectionsPooly18 Sep
    • mysql_free_result() CRASHESMiguel Cardenas18 Sep
    • Re: mysql_free_result() & 2 different connectionsMiguel Cardenas20 Sep
      • Re: mysql_free_result() & 2 different connectionsPooly20 Sep
        • Re: mysql_free_result() & 2 different connectionsMiguel Cardenas20 Sep
          • Re: mysql_free_result() & 2 different connectionsPooly20 Sep
            • Re: mysql_free_result() & 2 different connectionsMiguel Cardenas21 Sep
              • Re: mysql_free_result() & 2 different connectionsPooly21 Sep
                • Re: mysql_free_result() & 2 different connectionsMiguel Cardenas22 Sep