linux下C连接mysql

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以下变量类型在MySQL的库当中定义。我们需要这些变量是为了使用MySQL的函数。这些变量有详细的解释，但是这些解释对于写代码来说并不重要。

MYSQL
以下代码块是用来连接数据库的通讯过程

typedef struct st_mysql {  NET           net;            /* Communication parameters */  gptr          connector_fd;   /* ConnectorFd for SSL */  char          *host,*user,*passwd,*unix_socket,                *server_version,*host_info,*info,*db;  unsigned int  port,client_flag,server_capabilities;  unsigned int  protocol_version;  unsigned int  field_count;  unsigned int  server_status;  unsigned long thread_id;      /* Id for connection in server */  my_ulonglong affected_rows;  my_ulonglong insert_id;       /* id if insert on table with NEXTNR */  my_ulonglong extra_info;              /* Used by mysqlshow */  unsigned long packet_length;  enum mysql_status status;  MYSQL_FIELD   *fields;  MEM_ROOT      field_alloc;  my_bool       free_me;        /* If free in mysql_close */  my_bool       reconnect;      /* set to 1 if automatic reconnect */  struct st_mysql_options options;  char          scramble_buff[9];  struct charset_info_st *charset;  unsigned int  server_language;} MYSQL;

MYSQL_RES
这段代码返回查询结果的行。返回的数据称为“数据集”

typedef struct st_mysql_res {  my_ulonglong row_count;  unsigned int  field_count, current_field;  MYSQL_FIELD   *fields;  MYSQL_DATA    *data;  MYSQL_ROWS    *data_cursor;  MEM_ROOT      field_alloc;  MYSQL_ROW     row;            /* If unbuffered read */  MYSQL_ROW     current_row;    /* buffer to current row */  unsigned long *lengths;       /* column lengths of current row */  MYSQL         *handle;        /* for unbuffered reads */  my_bool       eof;            /* Used my mysql_fetch_row */} MYSQL_RES;

MYSQL_ROW
这个结构是数据行的一个安全表示法。你无法使用以空字符结束的串，因为数据在这个串可以是二进制, 也许没有包括任何字符。

typedef struct st_mysql_field {  char *name;                   /* Name of column */  char *table;                  /* Table of column if column was a field */  char *def;                    /* Default value (set by mysql_list_fields) */  enum enum_field_types type;   /* Type of field. Se mysql_com.h for types */  unsigned int length;          /* Width of column */  unsigned int max_length;      /* Max width of selected set */  unsigned int flags;           /* Div flags */  unsigned int decimals;        /* Number of decimals in field */} MYSQL_FIELD;

my_ulonglong
该类型用于行数，mysql_affected_rows() 、mysql_num_rows()和mysql_insert_id() 。该类型提供范围0 到1.84.e19 的支持。在一些系统, 试图打印出my_ulonglong类型的值是不行的.要显示这样的值, 使用%lu printf 格式，把它转换成unsigned long类型就行了。例如:
printf(Number of rows: %lu/n", (unsigned long) mysql_num_rows(result));

typedef unsigned long my_ulonglong;

一些有用的函数

看看如何取得一个表格的字段，以下这个函数可能实现这个功能：

unsigned int STDCALL mysql_num_fields(MYSQL *mysql);

这个函数返回表格里有多少个字段。

取得“数据集”的数目，用：

my_ulonglong STDCALL mysql_num_rows(MYSQL_RES *res);

my_ulonglong STDCALL mysql_affected_rows(MYSQL *mysql);

这个函数是用来得到受INSERT, DELETE, UPDATE查询语句影响的“数据集”数目。注意该函数返回的数据类型是my_ulonglong

一些示例代码：

＃i nclude <mysql/mysql.h>＃i nclude <stdio.h>void main(){   MYSQL *mysql;   MYSQL_RES *res;   MYSQL_ROW row;   char *query;   int t,r;   mysql_init(mysql);   if (!mysql_real_connect(mysql,"localhost","mysql",        "mysql","deneme",0,NULL,0))   {       printf( "Error connecting to database: %s/n",mysql_error(mysql));   }   else printf("Connected.../n");   query="select * from Deneme";   t=mysql_real_query(mysql,query,(unsigned int) strlen(query));   if (t)   {      printf("Error making query: %s/n",              mysql_error(mysql));   }   else printf("Query made.../n");   res=mysql_use_result(mysql);   for(r=0;r<=mysql_field_count(mysql);r++){           row=mysql_fetch_row(res);           if(row<0) break;           for(t=0;t<mysql_num_fields(res);t++){                   printf("%s ",row[t]);           }           printf("/n");   }   mysql_close(mysql);}

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ChinaUnix odin_free 今天给新来的同事做mysql培训，用到的一个例子： 连接数据库test 用户名root密码abc 在里面有一个username的表，describe username结果如下 mysql> describe username; +----------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------+-------------+------+-----+---------+-------+ | id | int(10) | YES | | NULL | | | username | varchar(32) | | PRI | | | +----------+-------------+------+-----+---------+-------+ mysql> select * from username; +------+----------+ | id | username | +------+----------+ | 1 | sfs | +------+----------+ 1 row in set (0.00 sec) 本文目的查找执行select id from username这个语句并打印结果 代码: ＃i nclude <unistd.h> ＃i nclude <arpa/inet.h> ＃i nclude <stdio.h> ＃i nclude <stdlib.h> ＃i nclude <string.h> ＃i nclude <sys/types.h> ＃i nclude <sys/socket.h> ＃i nclude <netinet/in.h> ＃i nclude <mysql/mysql.h> ＃i nclude <signal.h> ＃i nclude <errno.h> ＃i nclude <syslog.h> MYSQL mysql; main() {    char host[32]="localhost";    char user[32]="root";    char passwd[32]="abc";    char dbname[32]="test";             if( mysql_init(&mysql) == NULL )    {       syslog(LOG_USER|LOG_INFO,"inital mysql handle error/n");       return 1;    }    if (mysql_real_connect(&mysql,host,user,passwd,dbname,0,NULL,0) == NULL)    {       syslog(LOG_USER|LOG_INFO, "Failed to connect to database: Error: %s/n",mysql_error(&mysql));       return 1;    }    else syslog(LOG_USER|LOG_INFO, "connect to database: /n");    find_ps();        db_close();    return 0; } int db_close() {         mysql_close(&mysql);          return 0; } int  find_ps () {    MYSQL_ROW m_row;    MYSQL_RES *m_res;    char sql[1024],username[32];    int res=1;    int *id;    sprintf(sql,"select id from username");    if(mysql_query(&mysql,sql) != 0)    {       syslog(LOG_USER|LOG_INFO, "select ps_info Error: %s/n",mysql_error(&mysql));       return res;    }    m_res = mysql_store_result(&mysql);    if(m_res==NULL)    {       syslog(LOG_USER|LOG_INFO, "select username Error: %s/n",mysql_error(&mysql));       res = 3;       return res;    }    if(m_row = mysql_fetch_row(m_res))    {       printf("m_row=%d/n",atoi(m_row[0]));       res = 0;          }    mysql_free_result(m_res);    return res; } 编译命令 gcc -g connect_db.c -L/usr/lib/mysql -lmysqlclient -lz 注意： 如果/tmp/ccTGmMS21.o: In function `main': /tmp/ccTGmMS21.o(.text+0x11): undefined reference to `mysql_init' 那么参数增加-L/usr/lib/mysql -lmysqlclient 如果 usr/lib/mysql/libmysqlclient.a(my_compress.o): In function `my_uncompress': my_compress.o(.text+0xaa): undefined reference to `uncompress' 那么增加-lz参数

编译和连接程序

　　MySQL中有一个特殊的脚本,叫做mysql_config. 它会为你编译MySQL客户端,并连接到MySQL服务器提供有用的信息.你需要使用下面两个选项.

　　1. --libs 选项 - 连接MySQL客户端函数库所需要的库和选项.

　　$ mysql_config --libs

　　输出:

　　-L/usr/lib64/mysql -lmysqlclient -lz -lcrypt -lnsl -lm -L/usr/lib64 -lssl -lcrypto

　　2. --cflags 选项 - 使用必要的include文件的选项等等.

　　$ mysql_config --cflags

　　输出:

　　-I/usr/include/mysql -g -pipe -m64 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -fno-strict-aliasing

　　你需要将上面两个选项加入到对源文件的编译命令中. 所以,要编译上面的程序,要使用下面的命令:

　　$ gcc -o output-file $(mysql_config --cflags) mysql-c-api.c $(mysql_config --libs)

　　执行编译后的程序:

　　$ ./output.file