Question

Recently, I started to work on a C program that makes use of the libmysqlclient. When checking my code with valgrind, it reported memory leaks. The following minimal code snippet reproduces the behavior:

#include <mysql.h>

int main(void)
{
    MYSQL* mysql = mysql_init(0);

    mysql_close(mysql);

    return 0;
}

Checking the resulting program with valgrind tells me:

==25614== LEAK SUMMARY:
==25614==    definitely lost: 0 bytes in 0 blocks
==25614==    indirectly lost: 0 bytes in 0 blocks
==25614==      possibly lost: 0 bytes in 0 blocks
==25614==    still reachable: 288 bytes in 3 blocks
==25614==         suppressed: 0 bytes in 0 blocks

According to the MySQL API Reference, mysql_close()…

Closes a previously opened connection. mysql_close() also deallocates the connection handle pointed to by mysql if the handle was allocated automatically by mysql_init() or mysql_connect().

However, valgrind reports un-freed memory. What’s wrong here?

Answer 1

Digging through the docs, I found the function mysql_library_end() that solves the issue.

Citing from the MySQL API Reference:

This function finalizes the MySQL library. You should call it when you are done using the library (for example, after disconnecting from the server).

On a personal note, I find it rather annoying that libmysqlclient forces its users to call its own cleanup function. IMO, a nicer solution would be to call mysql_library_end() automatically whenever the connection count drops to zero.