看了下mysql的API，访问数据库也不是太难，当然啥都是看起来容易，做起来难
Windows开发环境不太熟，懒的去配置一堆东西，而且我mysql所有头文件和库文件都存在E盘，我就借用Cygwin，将头文件和库文件copy到相应的/usr/include和/usr/lib目录下，通过GCC来进行编译，进而运行进行访问
（1）mysql_init初始化连接句柄
#include <mysql.h> MYSQL *mysql_init(MYSQL *);
这里如果参数传递了一个已经存在的mysql数据结构，就会重新初始化；一般来说传递一个NULL给这个函数，会返回一个指向新分配的连接句柄结构的指针
（2）mysql_read_connect实际连接
上面仅仅是分配和初始化了一个结构，还需要提供实际参数来进行实际连接，mysql.h里
MYSQL *mysql_real_connect(MYSQL *connection,
const char *server_host, const char *sql_user_name, const char *sql_password, const char *db_name, unsigned int port_number, const char *unix_socket_name, unsigned int flags);
参数指针connection必须指向已经被mysql_init初始化过的结构；server_host既可以是主机名也可以是IP地址；sql_user_name和sql_password是数据库用户名和密码；然后是访问的数据库名，端口号，unix_socket_name为NULL；flags用来对一些定义的位模式进行OR操作，使得改变使用协议的某些特性，这个不太明白，先不管，设置为0
如果无法正常连接，函数就会返回NULL
（3）mysql_close关闭连接
所以，就直接访问新创建的数据库newbase：
mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | mysql | | newbase | | test | +--------------------+ 4 rows in set (0.00 sec)
来了一段：
#include <stdio.h>
#include <stdlib.h>
#include <mysql.h>
int main(){
MYSQL *conn_ptr;
conn_ptr = mysql_init(NULL);
if (!conn_ptr){
printf("mysql_init failed\n");
exit(0);
}
conn_ptr = mysql_real_connect(conn_ptr, "localhost", "root", "xxxx", "newbase", 3306, NULL, 0);
if (conn_ptr)
printf("Connection successful!\n");
else
printf("Connection failed\n");
mysql_close(conn_ptr);
return 0;
}
可是各种库，各种依赖都处理好了，运行结果就是failed，连接失败：
lihui@2015 /cygdrive/e/mysql/mysql-5.6.22-winx64
$ gcc -g -I/usr/include/mysql lihui.c -L/usr/lib/mysql -lmysqlclient -o connect
lihui@2015 /cygdrive/e/mysql/mysql-5.6.22-winx64
$ ./connect.exe
Connection failed
我在想是否是权限问题，于是CMD里来执行可执行程序：
E:\mysql\mysql-5.6.22-winx64\bin>connect.exe
Connection failed
这下就技穷了，gdb了一把，果然还是实际连接的时候出的问题，不知道是不是我这种连接方式就有问题
8 if (!conn_ptr){
(gdb) n
12 conn_ptr = mysql_real_connect(conn_ptr, "localhost", "root", "xxxx", "newbase", 3306, NULL, 0);
(gdb) p *conn_ptr
$1 = {net = {vio = 0x0, buff = 0x0, buff_end = 0x0, write_pos = 0x0, read_pos = 0x0, fd = 0, remain_in_buf = 0,
length = 0, buf_length = 0, where_b = 0, max_packet = 0, max_packet_size = 0, pkt_nr = 0, compress_pkt_nr = 0,
write_timeout = 0, read_timeout = 0, retry_count = 0, fcntl = 0, return_status = 0x0, reading_or_writing = 0 '\000',
save_char = 0 '\000', unused1 = 0 '\000', unused2 = 0 '\000', compress = 0 '\000', unused3 = 0 '\000', unused = 0x0,
last_errno = 0, error = 0 '\000', unused4 = 0 '\000', unused5 = 0 '\000', last_error = '\000' <repeats 511 times>,
sqlstate = "00000", extension = 0x0}, connector_fd = 0x0, host = 0x0, user = 0x0, passwd = 0x0, unix_socket = 0x0,
server_version = 0x0, host_info = 0x0, info = 0x0, db = 0x0, charset = 0x3eca56160 <my_charset_latin1>, fields = 0x0,
field_alloc = {free = 0x0, used = 0x0, pre_alloc = 0x0, min_malloc = 0, block_size = 0, block_num = 0,
first_block_usage = 0, error_handler = 0x0}, affected_rows = 0, insert_id = 0, extra_info = 0, thread_id = 0,
packet_length = 0, port = 0, client_flag = 0, server_capabilities = 0, protocol_version = 0, field_count = 0,
server_status = 0, server_language = 0, warning_count = 0, options = {connect_timeout = 0, read_timeout = 0,
write_timeout = 0, port = 0, protocol = 0, client_flag = 0, host = 0x0, user = 0x0, password = 0x0,
unix_socket = 0x0, db = 0x0, init_commands = 0x0, my_cnf_file = 0x0, my_cnf_group = 0x0, charset_dir = 0x0,
charset_name = 0x0, ssl_key = 0x0, ssl_cert = 0x0, ssl_ca = 0x0, ssl_capath = 0x0, ssl_cipher = 0x0,
shared_memory_base_name = 0x0, max_allowed_packet = 0, use_ssl = 0 '\000', compress = 0 '\000',
named_pipe = 0 '\000', unused1 = 0 '\000', unused2 = 0 '\000', unused3 = 0 '\000', unused4 = 0 '\000',
methods_to_use = MYSQL_OPT_GUESS_CONNECTION, client_ip = 0x0, secure_auth = 0 '\000',
report_data_truncation = 1 '\001', local_infile_init = 0x0, local_infile_read = 0x0, local_infile_end = 0x0,
local_infile_error = 0x0, local_infile_userdata = 0x0, extension = 0x0}, status = MYSQL_STATUS_READY,
free_me = 1 '\001', reconnect = 0 '\000', scramble = '\000' <repeats 20 times>, unused1 = 0 '\000', unused2 = 0x0,
unused3 = 0x0, unused4 = 0x0, unused5 = 0x0, stmts = 0x0, methods = 0x0, thd = 0x0, unbuffered_fetch_owner = 0x0,
info_buffer = 0x0, extension = 0x0}
(gdb) n
14 if (conn_ptr)
(gdb) p *conn_ptr
Cannot access memory at address 0x0
(gdb)
睡了，有空再找找原因 ~！
