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Editorial Team
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Asked: 2026-06-18T08:08:21+00:00

I am writing a daemon in C++, it has a simple task of inserting

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I am writing a daemon in C++, it has a simple task of inserting some events into a mysql database.

When I ran the top command I saw that the processe’s memory needs increase, I thought I had a memory leak and I started using Valgrind

I ran valgrind as this:

valgrind –tool=memcheck –leak-check=yes –show-reachable=yes
–num-callers=20 –track-fds=yes ./my_app

I get the following report:

==17045== 128 bytes in 1 blocks are definitely lost in loss record 6 of 11
==17045==    at 0x402A629: calloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==17045==    by 0x40AAB63: my_thread_init (in /usr/lib/i386-linux-gnu/libmysqlclient.so.18.0.0)
==17045==    by 0x40AAE43: my_thread_global_init (in /usr/lib/i386-linux-gnu/libmysqlclient.so.18.0.0)
==17045==    by 0x40A92D7: my_init (in /usr/lib/i386-linux-gnu/libmysqlclient.so.18.0.0)
==17045==    by 0x40863FA: mysql_server_init (in /usr/lib/i386-linux-gnu/libmysqlclient.so.18.0.0)
==17045==    by 0x4087B28: mysql_init (in /usr/lib/i386-linux-gnu/libmysqlclient.so.18.0.0)
==17045==    by 0x8049890: write_db(std::string, std::string, std::string) (Listener.cpp:76)
==17045==    by 0x804A692: SocketListener(void*) (Listener.cpp:182)
==17045==    by 0x4052D4B: start_thread (pthread_create.c:308)
==17045==    by 0x4582D3D: clone (clone.S:130)

The function write_db is this:

void write_db(std::string userid,std::string zona,std::string eveniment)
{
    try
    {
    MYSQL * connect;
    connect = mysql_init(NULL);
    connect = mysql_real_connect(connect,"127.0.0.1","myusr","mypwd","mytbl",0,NULL,0);
    std::string stmt = "INSERT INTO t_evenimente(placaid,codev,zona,cand) VALUES(\"" + userid + "\"," + eveniment + ",\"" + zona + "\",NOW())";
    std::cout << stmt << std::endl;
    mysql_query(connect,stmt.c_str());
    mysql_close(connect);
    std::cout << "Inserat eveniment obiectiv " << userid << std::endl;
    }
    catch (...)
    {
        std::cout <<"Exceptie MYSQL" << std::endl;
    }
}

Where is the memory leak ? I am using mysql_init and close as the documentation says…Could it be a false positive ?

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1 Answer

  1. Editorial Team

    Since you’re using connect only inside your function, it’s easier not to allocate it dynamically and risk a memory leak (most likely the one you’re seeing). Also, the MySQL API is a C API and does not throw any exceptions for you to catch, which will simplify what you have now down to something like;

    void write_db(std::string userid,std::string zona,std::string eveniment)
{
    MYSQL connect;
    mysql_init(&connect);
    mysql_real_connect(&connect,"127.0.0.1","myusr","mypwd","mytbl",0,NULL,0);
    std::string stmt = "INSERT INTO t_evenimente(placaid,codev,zona,cand) VALUES(\"" + userid + "\"," + eveniment + ",\"" + zona + "\",NOW())";
    std::cout << stmt << std::endl;
    mysql_query(&connect,stmt.c_str());
    mysql_close(&connect);
    std::cout << "Inserat eveniment obiectiv " << userid << std::endl;
}

    Of course, that still leaves out error handling, which you’ll need to add back.

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