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On an Amazon EC2 (uname -r gives "3.4.37-40.44.amzn1.x86_64", which I hear is based on Cent OS) I tried installing:

yum install mysql
yum install mysql-devel

And even

yum install mysql-libs

(Due to this thread.)

I'm trying to compile a program and link the MySQL libraries to it. This works fine on my Mac, (but the Mac has libmysqlclient.a). libmysqlclient.a is absolutely nowhere to be found on this machine. All it has is libmysqlclient.so, and many versions of it too.

$ sudo find / -name libmysqlclient*

Gives

/usr/lib64/mysql/libmysqlclient_r.so
/usr/lib64/mysql/libmysqlclient.so
/usr/lib64/mysql/libmysqlclient.so.18
/usr/lib64/mysql/libmysqlclient.so.18.0.0
/etc/alternatives/libmysqlclient
/etc/alternatives/libmysqlclient_r

And

ls -l /usr/lib64/mysql

Gives

lrwxrwxrwx 1 root root      34 Apr 11 19:21 libmysqlclient_r.so -> /etc/alternatives/libmysqlclient_r
lrwxrwxrwx 1 root root      32 Apr 11 19:21 libmysqlclient.so -> /etc/alternatives/libmysqlclient
lrwxrwxrwx 1 root root      24 Apr 11 18:24 libmysqlclient.so.18 -> libmysqlclient.so.18.0.0
-rwxr-xr-x 1 root root 2983360 Mar 14 10:09 libmysqlclient.so.18.0.0
-rwxr-xr-x 1 root root   11892 Mar 14 09:12 mysqlbug
-rwxr-xr-x 1 root root    7092 Mar 14 10:08 mysql_config

So the only real file is libmysqlclient.so.18.0.0.

The compiler command:

g++ main.cpp -L/usr/lib64/mysql -lmysqlclient.so.18.0.0

Fails with

/usr/bin/ld: cannot find -lmysqlclient.so.18.0.0
collect2: ld returned 1 exit status

So somebody is lying or I got completely ripped off at the YUM repo and was not given my libmysqlclient.a like I was supposed to.

(I avoided using the many symlinks on the system so I could eliminate possible issues).

user207421
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bobobobo
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2 Answers2

2

bobobobo! You are so wrong.

First of all, you don't need a libmysqlclient.a file, when you have the .so file. The .a file is for static linking, .so file for dynamic linking.. .so files are decidely better and make you cool.

The problem you get when you try and compile without library link is 

g++ main.cpp

Gives

undefined reference to `mysql_init'

But that can be fixed with

g++ main.cpp `mysql_config --cflags --libs`
Community
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bobobobo
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  • You know what would be cool? If I could link against a static version of libmysqlclient so I don't have to rebuild my code when I try to run on a system that doesn't have the same version installed. libmysqlclient.so also brings along a dependency on other dynamic libraries which compounds the issue. – CoAstroGeek Jun 18 '21 at 22:57
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When you use .so, they are linked a run-time. This makes your compiled code smaller. Not usually big deal these days. The really great feature is that when you update your system, and the library gets updated, you will link in the new (and hopefully) better library. The updates often contain bug fixes and security fixes. Possibly performance improvements. Therefore they make your code more cool and, indirectly, make you a little bit more cool.

Chris VanWyk
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  • ...but it also means the library can update to be incompatible, or just get EOLed and go missing. Staticly linked libraries are always there. – Zds Oct 02 '15 at 11:36