CentOS7 (64位) 下QT5.5 连接MySQL数据库（driver not loaded）用qt连接MySQL需要共享库 libqsqlmysql.so的驱动，路径在plugin/sqldrivers目录下，乍看已经可用了，其实不然。
用ldd命令分析一下，libmysqlclient_r.so.16 => not found ,后明显libmysqlclient_r.so.16 缺少另一个共享库，他们是依赖关系，解决了这个问题qt才能真的连接到mysql数据库。而我的/usr/lib64/下的共享库版本比较高是libmysqlclient.so.18，想到了一个比较投机的想法ln创建符号链接，然而这并没有什么卵用。
让我哭笑不得是QT5.5是我从官网下载的，居然依赖的是低版本，你们编译的时候能不能不偷懒啊，估计他们直接从低版本拷贝的libqsqlmysql.so，没办法了吗？显然不是，打开qt官网下载源码，自己编译。下载过程略过，非常好找http://download.qt.io/official_releases/qt/5.4/5.4.2/submodules/ （暂时没有qt5.5的源码），找到qtbase那个大概60M。MySql驱动的路径为qtbase/src/plugins/sqldrivers/mysql/。
qmakemake然而这还没有完，make的过程中又找不到动态库了：
/usr/bin/ld: cannot find -lz/usr/bin/ld: cannot find -lssl/usr/bin/ld: cannot find -lcrypto
第一个是没有安装zlib-devel，直接yum install zlib-devel搞定。
第二第三项找不到是没有道理的，解决的方法：/usr/lib64/中创建符号链接
ln -s libssl.so.1.0.1e libssl.soln -s libcrypto.so.1.0.1e libcrypto.so
再次make，成功。当然这还没有完，用新的libqsqlmysql.so去替换旧的，这就全部完成了。
再次查看：
[sqldrivers]ldd libqsqlmysql.so linux-vdso.so.1 => (0x00007fff2d5fe000) libmysqlclient.so.18 => /usr/lib64/mysql/libmysqlclient.so.18 (0x00007feb4ea24000) libz.so.1 => /lib64/libz.so.1 (0x00007feb4e80d000) libcrypt.so.1 => /lib64/libcrypt.so.1 (0x00007feb4e5d6000) libnsl.so.1 => /lib64/libnsl.so.1 (0x00007feb4e3bd000) libssl.so.10 => /lib64/libssl.so.10 (0x00007feb4e150000) libcrypto.so.10 => /lib64/libcrypto.so.10 (0x00007feb4dd6b000) libQt5Sql.so.5 => /home/eric/Qt5.5.0/5.5/gcc_64/lib/libQt5Sql.so.5 (0x00007feb4db2b000) libQt5Core.so.5 => /home/eric/Qt5.5.0/5.5/gcc_64/lib/libQt5Core.so.5 (0x00007feb4d3e3000) libpthread.so.0 => /lib64/libpthread.so.0 (0x00007feb4d1c7000) libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007feb4cec0000) libm.so.6 => /lib64/libm.so.6 (0x00007feb4cbbd000) libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007feb4c9a7000) libc.so.6 => /lib64/libc.so.6 (0x00007feb4c5e6000) libdl.so.2 => /lib64/libdl.so.2 (0x00007feb4c3e1000) libfreebl3.so => /lib64/libfreebl3.so (0x00007feb4c164000) libgssapi_krb5.so.2 => /lib64/libgssapi_krb5.so.2 (0x00007feb4bf1a000) libkrb5.so.3 => /lib64/libkrb5.so.3 (0x00007feb4bc39000) libcom_err.so.2 => /lib64/libcom_err.so.2 (0x00007feb4ba35000) libk5crypto.so.3 => /lib64/libk5crypto.so.3 (0x00007feb4b800000) libicui18n.so.54 => /home/eric/Qt5.5.0/5.5/gcc_64/lib/libicui18n.so.54 (0x00007feb4b391000) libicuuc.so.54 => /home/eric/Qt5.5.0/5.5/gcc_64/lib/libicuuc.so.54 (0x00007feb4afe3000) libicudata.so.54 => /home/eric/Qt5.5.0/5.5/gcc_64/lib/libicudata.so.54 (0x00007feb495b9000) libgthread-2.0.so.0 => /lib64/libgthread-2.0.so.0 (0x00007feb493b6000) librt.so.1 => /lib64/librt.so.1 (0x00007feb491ae000) libglib-2.0.so.0 => /lib64/libglib-2.0.so.0 (0x00007feb48e85000) /lib64/ld-linux-x86-64.so.2 (0x00007feb4f221000) libkrb5support.so.0 => /lib64/libkrb5support.so.0 (0x00007feb48c76000) libkeyutils.so.1 => /lib64/libkeyutils.so.1 (0x00007feb48a72000) libresolv.so.2 => /lib64/libresolv.so.2 (0x00007feb48858000) libselinux.so.1 => /lib64/libselinux.so.1 (0x00007feb48632000) libpcre.so.1 => /lib64/libpcre.so.1 (0x00007feb483d1000) liblzma.so.5 => /lib64/liblzma.so.5 (0x00007feb481ab000)
