cmake:用于搜索mysql的FindMySQL.cmake及bug溯源及修复
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最近设计一个需要mysql的项目,构建项目的时候需要find_package查找mysql 库安装位置，cmake默认没有提供mysql的find_package支持.好在mysql官方是提供了，在github上mysql-connector-odbc项目找到了FindMySQL.cmake:
https://github.com/mysql/mysql-connector-odbc/blob/master/cmake/FindMySQL.cmake
有它就好办了。
CMakeLists中添加mysql库支持
在CMakeLists.txt 添加如下代码
# 查找 MySQL SDK
#set(MYSQLCLIENT_STATIC_LINKING true)
#set(FINDMYSQL_DEBUG true)
find_package(MySQL MODULE REQUIRED)
设置环境变量MYSQL_DIR
如下是FindMySQL.cmake源码中关于可选参数的说明：
##########################################################################
#
# Configuration variables, all optional, are
#
# MYSQL_DIR - Set in environment or as parameter to "cmake",
# this is the top directory of the MySQL Server or
# Connector/C install
# MYSQL_INCLUDE_DIR - Set in environment or as parameter to "cmake",
# this is the include directory where to find
# the client library
# MYSQL_LIB_DIR - Set in environment or as parameter to "cmake",
# this is the library directory where to find
# the client library
# MYSQLCLIENT_STATIC_LINKING
# - Specify that you want static linking, dynamic
# linking is the default
# MYSQLCLIENT_NO_THREADS
# - Specify to link against the single threaded
# library, "libmysqlclient". Note that in 5.5
# and up "libmysqlclient" is multithreaded and
# "libmysqlclient_r" just a soft link to it
# MYSQL_CONFIG_EXECUTABLE
# - "mysql_config" executable to use
# MYSQL_CXX_LINKAGE - Specify that client library needs C++ linking
# MYSQL_EXTRA_LIBRARIES
# - Libraries to add to the linkage
# MYSQL_CFLAGS - C compiler flags
# MYSQL_CXXFLAGS - C++ compiler flags
# MYSQL_LINK_FLAGS - User defined extra linkage flags
# FINDMYSQL_DEBUG - Set if want debug output from this script
通过上面的代码可知，FindMySQL允许通过环境变量或参数MYSQL_DIR来指定MySQL Server的安装位置。所以windows下可以通过如下脚本查找mysqld,计算mysql-server的安装位置，并设置MYSQL_DIR环境变量，然后
where mysqld
if errorlevel 1 (
echo mysqld NOT FOUND.
exit /B -1
)
echo mysqld found
:: 获取mysql安装路径
FOR /F "delims=*" %%i in ('where mysqld') do set mysqld_bin=%%~dpi
::echo mysqld_bin=%mysqld_bin%
:: 删除最后的 '\\'
set mysqld_bin=%mysqld_bin:~0,-1%
::echo mysqld_bin=%mysqld_bin%
for /f "delims=*" %%i in ("%mysqld_bin%") DO set MYSQL_DIR=%%~dpi
::echo MYSQL_DIR=%MYSQL_DIR%
:: 设置MYSQL_DIR环境变量
set MYSQL_DIR=%MYSQL_DIR:~0,-1%
echo MYSQL_DIR=%MYSQL_DIR%
执行
:: 生成Visual Studio 2015工程
cmake . -G "Visual Studio 14 2015 Win64"
如果执行成功就会看到如下输出
-- You will link dynamically to the MySQL client library (set with -DMYSQLCLIENT_STATIC_LINKING=<bool>)
-- Searching for dynamic libraries with the base name(s) "libmysql"
-- MYSQL_LIB_DIR_LIST =
-- MySQL client environment/cmake variables set that the user can override
-- MYSQL_DIR : D:/mysql-5.6.37-winx64
-- MYSQL_INCLUDE_DIR : D:/mysql-5.6.37-winx64/include
-- MYSQL_LIB_DIR : D:/mysql-5.6.37-winx64/lib
-- MYSQL_PLUGIN_DIR : D:/mysql-5.6.37-winx64/lib/plugin
-- MYSQL_CONFIG_EXECUTABLE :
-- MYSQL_CXX_LINKAGE :
-- MYSQL_CFLAGS :
-- MYSQL_CXXFLAGS :
-- MYSQLCLIENT_STATIC_LINKING :
-- MYSQLCLIENT_NO_THREADS :
-- MySQL client optional environment/cmake variables set by the user
-- MYSQL_EXTRA_LIBRARIES :
-- MYSQL_LINK_FLAGS :
-- MySQL client settings that the user can't override
-- MYSQL_VERSION : 5.6.37
-- MYSQL_VERSION_ID : 50637
-- MYSQL_LIB : D:/mysql-5.6.37-winx64/lib/libmysql.lib
-- MYSQL_LIBRARIES : mysql_sys;mysql_strings;D:/mysql-5.6.37-winx64/lib/libmysql.lib
BUG
然而事实上你会看到如下输出：
-- You will link dynamically to the MySQL client library (set with -DMYSQLCLIENT
_STATIC_LINKING=<bool>)
-- Searching for dynamic libraries with the base name(s) "libmysql"
CMake Error at cmake/Modules/FindMySQL.cmake:824 (message):
Could not determine the MySQL Server version
Call Stack (most recent call first):
src/CMakeLists.txt:8 (find_package)
Could not determine the MySQL Server version 出错啦!
同样的代码在linux下却是正常的。
这可是官方提供的FindMySQL.cmake脚本哦，难道有Bug?
问题溯源
进一步阅读FindMySQL.cmake的源码，找到如下位置
if(MYSQL_INCLUDE_DIR AND NOT MYSQL_VERSION)
# Write the C source file that will include the MySQL headers
set(GETMYSQLVERSION_SOURCEFILE "$CMAKE_CURRENT_BINARY_DIR/getmysqlversion.c")
file(WRITE "$GETMYSQLVERSION_SOURCEFILE"
"#include <mysql.h>\\n"
"#include <stdio.h>\\n"
"int main() \\n"
" printf(\\"%s\\", MYSQL_SERVER_VERSION);\\n"
"\\n"
)
# Compile and run the created executable, store output in MYSQL_VERSION
try_run(_run_result _compile_result
"$CMAKE_BINARY_DIR"
"$GETMYSQLVERSION_SOURCEFILE"
CMAKE_FLAGS "-DINCLUDE_DIRECTORIES:STRING=$MYSQL_INCLUDE_DIR"
RUN_OUTPUT_VARIABLE MYSQL_VERSION
)
if(FINDMYSQL_DEBUG)
if(NOT _compile_result)
message("DBG: Could not compile \\"getmysqlversion.c\\"")
endif()
if(_run_result)
message("DBG: Running \\"getmysqlversion\\" returned $_run_result")
endif()
endif()
endif()
可以看到FindMySQL.cmake为了获取mysql版本号，临时生成了一个getmysqlversion.c文件编译并执行它，通过getmysqlversion.exe的输出获取msyql.h中定义的MYSQL_SERVER_VERSION。
getmysqlversion.c
#include <mysql.h>
#include <stdio.h>
int main()
printf("%s", MYSQL_SERVER_VERSION);
于是我在cmake生成的工程文件中找到getmysqlversion.c，在命令行对它用MSVC的cl编译器进行编译
cl getmysqlversion.c /I d:\\mysql-5.6.37-winx64\\include
果然报错了
用于 x64 的 Microsoft (R) C/C++ 优化编译器 19.00.24215.1 版
版权所有(C) Microsoft Corporation。保留所有权利。
getmysqlversion.c
d:\\mysql-5.6.37-winx64\\include\\mysql_com.h(321): error C2061: 语法错误: 标识符“
SOCKET”
d:\\mysql-5.6.37-winx64\\include\\mysql_com.h(365): error C2059: 语法错误:“”
d:\\mysql-5.6.37-winx64\\include\\mysql_com.h(482): error C2143: 语法错误: 缺少“)”(在“*”的前面)
d:\\mysql-5.6.37-winx64\\include\\mysql_com.h(482): error C2143: 语法错误: 缺少“”(在“*”的前面)
d:\\mysql-5.6.37-winx64\\include\\mysql_com.h(482): error C2371: “Vio”: 重定义；不同的基类型
d:\\mysql-5.6.37-winx64\\include\\mysql_com.h(307): note: 参见“Vio”的声明
d:\\mysql-5.6.37-winx64\\include\\mysql_com.h(482): error C2143: 语法错误: 缺少“;”(在“*”的前面)
d:\\mysql-5.6.37-winx64\\include\\mysql_com.h(482): error C2059: 语法错误:“)”
d:\\mysql-5.6.37-winx64\\include\\mysql_com.h(483): error C2143: 语法错误: 缺少“)”(在“*”的前面)
d:\\mysql-5.6.37-winx64\\include\\mysql_com.h(483): error C2143: 语法错误: 缺少“”(在“*”的前面)
....
d:\\mysql-5.6.37-winx64\\include\\mysql.h(404): fatal error C1003: 错误计数超过 100；正在停止编译
进一步分析mysql.h的源码，及MYSQL_SERVER_VERSION宏定义的位置，发现MYSQL_SERVER_VERSION其实定义在mysq_version.h中,而报错则与mysql_version.h不相关的mysql_com.h。所以实际上只需要include mysql_version.h
将#include <mysql.h>改为#include <mysql_version.h>则编译成功
getmysqlversion.c
#include <mysql_version.h>
#include <stdio.h>
int main()
printf("%s", MYSQL_SERVER_VERSION);
>cl getmysqlversion.c /I d:\\mysql-5.6.37-winx64\\include
用于 x64 的 Microsoft (R) C/C++ 优化编译器 19.00.24215.1 版
版权所有(C) Microsoft Corporation。保留所有权利。
getmysqlversion.c
Microsoft (R) Incremental Linker Version 14.00.24215.1
Copyright (C) Microsoft Corporation. All rights reserved.
/out:getmysqlversion.exe
getmysqlversion.obj
J:\\mysql-listener\\project.vs2015\\src>getmysqlversion.exe
5.6.37
哈哈，果然是个bug,于是将FindMySQL.cmake中对应的代码修改为,
file(WRITE "$GETMYSQLVERSION_SOURCEFILE"
"#include <mysql_version.h>\\n"
"#include <stdio.h>\\n"
"int main() \\n"
" printf(\\"%s\\", MYSQL_SERVER_VERSION);\\n"
"\\n"
)
再执行就会看到成功输出了
:: 生成Visual Studio 2015工程
cmake . -G "Visual Studio 14 2015 Win64"
Pull Request
上面的修改已经向mysql-connector-odbc官方提交PR:
如果被批准，则你可以从https://github.com/mysql/mysql-connector-odbc/blob/master/cmake/FindMySQL.cmake下载修复后的脚本，
否则要自己修改，或从https://gitee.com/l0km/mysql-listener/blob/master/cmake/Modules/FindMySQL.cmake下载修复后的脚本
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