当在C++代码中，直接引用MySQL头文件时，可能会遇到如下错误：

In file included from /usr/include/c++/4.1.0/bits/char_traits.h:46,
                 from /usr/include/c++/4.1.0/string:46,
/usr/include/c++/4.1.0/bits/stl_algobase.h:92:28: error: macro "swap" requires 3 arguments, but only 2 given
/usr/include/c++/4.1.0/bits/stl_algobase.h:127:26: error: macro "swap" requires 3 arguments, but only 2 given

/usr/include/c++/4.1.0/bits/vector.tcc:176:20: error: macro "swap" requires 3 arguments, but only 1 given
/usr/include/c++/4.1.0/cctype:70: error: '::isalnum' has not been declared
/usr/include/c++/4.1.0/cctype:71: error: '::isalpha' has not been declared
/usr/include/c++/4.1.0/cctype:72: error: '::iscntrl' has not been declared
/usr/include/c++/4.1.0/cctype:73: error: '::isdigit' has not been declared
/usr/include/c++/4.1.0/cctype:74: error: '::isgraph' has not been declared
/usr/include/c++/4.1.0/cctype:75: error: '::islower' has not been declared
/usr/include/c++/4.1.0/cctype:76: error: '::isprint' has not been declared
/usr/include/c++/4.1.0/cctype:77: error: '::ispunct' has not been declared
/usr/include/c++/4.1.0/cctype:78: error: '::isspace' has not been declared
/usr/include/c++/4.1.0/cctype:79: error: '::isupper' has not been declared
/usr/include/c++/4.1.0/cctype:80: error: '::isxdigit' has not been declared
/usr/include/c++/4.1.0/cctype:81: error: '::tolower' has not been declared
/usr/include/c++/4.1.0/cctype:82: error: '::toupper' has not been declared

解决办法：
尽量对MySQL进行二次包装，让调用者看不到MySQL头文件，如在CPP中包含：
#include <my_global.h>
#include <my_sys.h>
#include <mysql.h>


在头文件中只进行引用声明：
struct st_mysql;
struct st_mysql_res;

typedef long num_t;
typedef char ** MYSQL_ROW;  /** return data as array of strings */

不要在头文件直接include到MySQL的头文件，而且保证只在一个CPP文件中有对MySQL文件的include，否则你可能遇到很多莫名其妙的编译错误，如果不想到这一点，即使花一天时间也未必能找到错误原因。