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HomeDatabaseMysql TutorialMysql数据库学习(四):常用MysqlCAPI介绍和使用、封装一个访问_MySQL

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首先,环境是windows + vs2008,Mysql数据库已经安装好,在使用之前,需要配置工程属性,附加包含目录添加

D:/Program Files/MySQL/MySQL Server 5.6/include (Mysql安装目录),附加库目录添加 D:/Program Files/MySQL/MySQL Server 5.6/lib ,附加依赖项添加 mysqlib.lib,当然mysqllib.lib 只是包含符号而已,可执行文件运行的时候需要mysqllib.dll(lib目录下), 将其拷贝到exe同目录下。

一、常用Mysql C API 介绍和使用

1.mysql_init

MYSQL结构代表一个连接句柄 MYSQL*mysql_init(MYSQL*mysql); 如果mysql是NULL指针,该函数将分配、初始化、并返回新对象。否则,将初始化对象,并返回对象的地址。如果mysql_init()分配了新的对象,当调用mysql_close()来关闭连接时。将释放该对象。
2.mysql_real_connect
// 连接数据库 MYSQL *mysql_real_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd, const char *db, unsigned int port, const char *unix_socket, unsigned long client_flag)

//设置数据库
my_bool reconnect = true;
mysql_options(mysql, MYSQL_OPT_RECONNECT, &reconnect);
mysql_options(mysql, MYSQL_SET_CHARSET_NAME, "gbk");

3.mysql_query
int mysql_query(MYSQL *mysql, const char *query)
mysql_affected_rows
mysql_store_result
mysql_num_fields
mysql_num_rows
mysql_fetch_field
mysql_fetch_row
mysql_free_result

示例代码如下:
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#include
#include
#include

int main(void)
{
//初始化一个连接句柄
MYSQL* mysql = mysql_init(NULL);
if (mysql == NULL)
{
printf("error:%s", mysql_error(mysql));
return 1;
}

my_bool reconnect = true;
mysql_options(mysql, MYSQL_OPT_RECONNECT, &reconnect);
mysql_options(mysql, MYSQL_SET_CHARSET_NAME, "gbk");

if (!mysql_real_connect(mysql, "localhost", "root", "123456",
"scott", 0, NULL, 0))
{
printf("error:%s", mysql_error(mysql));
return 1;
}

// 没有返回结果集的操作
int result;
result = mysql_query(mysql, "insert into emp values(8888, 'YYYY', 'CLERK', 7782, '1990-04-10', 1500, NULL, 50);");
if (result != 0)
{
printf("error:%s", mysql_error(mysql));
return 1;
}
printf("%llu 行受影响/n", mysql_affected_rows(mysql));

// 有返回结果集的操作
result = mysql_query(mysql, "select * from emp where deptno=30;");
if (result != 0)
{
printf("error:%s", mysql_error(mysql));
return 1;
}

MYSQL_RES* mysql_res;
MYSQL_FIELD* mysql_field;
MYSQL_ROW mysql_row;
unsigned int cols;
mysql_res = mysql_store_result(mysql);
cols = mysql_num_fields(mysql_res);

if (mysql_res != NULL)
{
printf("返回%llu行/n", mysql_num_rows(mysql_res));
while((mysql_field = mysql_fetch_field(mysql_res)))
{
printf("%s/t", mysql_field->name);
}
printf("/n");

while((mysql_row = mysql_fetch_row(mysql_res)))
{
for (unsigned int i = 0; i {
printf("%s/t", mysql_row[i]? mysql_row[i]: "NULL");
}
printf("/n");
}
mysql_free_result(mysql_res);
}

mysql_close(mysql);
return 0;
}
输出结果如下,因为各字段值长短不一,虽然加了tab,输出还是有点别扭:
/


二、下面封装MysqlDB类
使用的基本是上面演示过的函数,就不多解释了,直接看代码吧。
MysqlDB.h: C++ Code 1
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  #ifndef _MYSQL_DB_H_
#define _MYSQL_DB_H_

//#define WIN32_LEAN_AND_MEAN
#include
#include

#include
#include
using namespace std;

namespace DAL
{

class MysqlDB;
class MysqlRecordset
{
friend class MysqlDB;
public:
const string& GetItem(unsigned int nRow, unsigned int nCol) const
{
return rows_[nRow][nCol];
}

const string& GetItem(unsigned int nRow, const string& name) const
{
unsigned int index = GetFieldIndex(name);
return rows_[nRow][index];
}

unsigned int GetRows() const
{
return rows_.size();
}

unsigned int GetCols() const
{
return fields_.size();
}

unsigned int GetFieldIndex(const std::string &name) const
{
unsigned int index = -1;
for(unsigned int i = 0; i {
if (fields_[i].name == name)
index = fields_[i].index;
}
return index;
}

void Clear()
{
rows_.clear();
fields_.clear();
}

typedef struct Field
{
string name; //列的字段名
unsigned int index; //字段名对应的下标
} FIELD;

typedef vector FIELDS; //所有列的字段结构体集合
typedef vector ROW; //每一行存储值

private:
vector rows_; // 总共存储多个行
FIELDS fields_;
};

class MysqlDB
{
public:
MysqlDB();
~MysqlDB();
void Open(const char* host,
const char* user,
const char* passwd,
const char* db,
unsigned int port);
void Close();

unsigned long long ExecSQL(const char* sql);
MysqlRecordset QuerySQL(const char* sql);

unsigned long long GetInsertId() const;
void StartTransaction();
void Commit();
void Rollback();


private:
MYSQL* mysql_;
};

}

#endif // _MYSQL_DB_H_
MysqlDB.cpp: C++ Code 1
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  #include
#include "MysqlDB.h"

using namespace std;

MysqlDB::MysqlDB() : mysql_(NULL)
{
}

MysqlDB::~MysqlDB()
{
if (mysql_)
{
Close();
}
}
void MysqlDB::Open(const char* host,
const char* user,
const char* passwd,
const char* db,
unsigned int port)
{

mysql_ = mysql_init(NULL);
if (mysql_ == NULL)
{
string errmsg = mysql_error(mysql_);
throw Exception("DB ERROR:"+errmsg);
}

my_bool reconnect = true;
mysql_options(mysql_, MYSQL_OPT_RECONNECT, &reconnect);
mysql_options(mysql_, MYSQL_SET_CHARSET_NAME, "gbk");

if (!mysql_real_connect(mysql_, host, user,
passwd, db, 0, NULL, 0))
{
string errmsg = mysql_error(mysql_);
Close();
throw Exception("DB ERROR:"+errmsg);
}
}

void MysqlDB::Close()
{
if (NULL != mysql_)
{
mysql_close(mysql_);
mysql_ = NULL;
}
}

MysqlRecordset MysqlDB::QuerySQL(const char* sql)
{
if (mysql_query(mysql_, sql) != 0)
{
//int errno = mysql_errno(mysql_);
string errmsg = mysql_error(mysql_);
throw Exception("DB ERROR:"+errmsg);
}

MYSQL_RES* mysql_res;
mysql_res = mysql_store_result(mysql_);

//得到查询返回的行数
//unsigned long n = mysql_affected_rows(mysql_);

//指向 mysql 的查询字段集
MYSQL_FIELD* mysql_field = NULL;

MysqlRecordset rs;
unsigned int i = 0;
unsigned int nCols = mysql_num_fields(mysql_res);
while ((mysql_field = mysql_fetch_field(mysql_res)) != NULL)
{
MysqlRecordset::FIELD field;
field.name = mysql_field->name;
field.index = i;
++i;
rs.fields_.push_back(field); //压入某个列字段的结构体
}

MYSQL_ROW mysql_row;
while ((mysql_row = mysql_fetch_row(mysql_res)))
{
MysqlRecordset::ROW row(nCols);
for (unsigned int i = 0; i {
row[i] = mysql_row[i] ? mysql_row[i] : "";
}
rs.rows_.push_back(row); //压入某一行的存储值

}


mysql_free_result(mysql_res);

return rs;

}

unsigned long long MysqlDB::ExecSQL(const char* sql)
{
if (mysql_query(mysql_, sql) != 0)
{
//int errno = mysql_errno(mysql_);
string errmsg = mysql_error(mysql_);
throw Exception("DB ERROR:"+errmsg);
}

return mysql_affected_rows(mysql_);

}

void MysqlDB::StartTransaction()
{
if (mysql_query(mysql_, "START TRANSACTION") != 0)
{
//int errno = mysql_errno(mysql_);
string errmsg = mysql_error(mysql_);
throw Exception("DB ERROR:"+errmsg);
}
}

void MysqlDB::Commit()
{
if (mysql_query( mysql_, "COMMIT") != 0)
{
//int errno = mysql_errno(mysql_);
string errmsg = mysql_error(mysql_);
throw Exception("DB ERROR:"+errmsg);
}
}

void MysqlDB::Rollback()
{
if (mysql_query(mysql_, "ROLLBACK") == 0)
{
//int errno = mysql_errno(mysql_);
string errmsg = mysql_error(mysql_);
throw Exception("DB ERROR:"+errmsg);
}
}


unsigned long long MysqlDB::GetInsertId() const
{
return mysql_insert_id(mysql_); //auto_increment字段
}
具体使用方法就很简单了,包含MysqlDB.h,比如 MysqlDB mysqldb; mysqldb.open(); mysqldb.QuerySQL(); ...

参考:

《数据库系统概论》

mysql 5.1 参考手册

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