How to create a shared object library (*.so) with mysql connector? - mysql

Question

I have written a very simple application in C, for which I would like to have a connection with MySQL database. Here is the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mysql.h>
#include <my_global.h>
void runtime_tile_opt(void);
int main(void) {
runtime_tile_opt();
return 0;
}
void runtime_tile_opt() {
printf("MySQL client version: %s\n", mysql_get_client_info());
}
If i run gcc -o runtime $(mysql_config --cflags) runtime.c $(mysql_config --libs), everything works fine, all libraries seemed to be properly linked, and if I run the executable, I get a legitimate-looking output:
MySQL client version: 5.5.49
However, I would like to make a shared library out of it. So I'm trying to create an object file, with -fPIC flag:
gcc -c -fPIC runtime.c $(mysql_config --cflags) -o runtime.o $(mysql_config --libs)
The outputs of mysql_config --libs mysql_config --cflags are:
-L/usr/lib/x86_64-linux-gnu -lmysqlclient -lpthread -lz -lm -ldl
-I/usr/include/mysql -DBIG_JOINS=1 -fno-strict-aliasing -g -DNDEBUG
Finally, I create my .so:
gcc runtime.o -shared -o runtime.so
All of the above went with no errors whatsoever. However, some library is not linked apparently, since when I run a file with this plugin loaded, I get:
/home/michal/thesis/Drafts/runtime/runtime.so: undefined reference to `mysql_get_client_info'
This function is defined in the header files I included. I'm not very experienced with gcc, but I look at it and it looks as though I linked what I had to link. Any ideas where did I fail?

Answer 1

You still need to pass the correct -l flags to the compiler when creating a shared library. They should be the same flags you pass when creating a binary, i.e.
gcc -shared -o runtime.so $(mysql_config --cflags) runtime.o $(mysql_config --libs)
Note that the order of options is important! First pass all options, then all files and lastly libraries (-l... operands).