C++封装MySQL预处理C API

#ifndef _PRE_STATEMENT_H_
#define _PRE_STATEMENT_H_

#include "mysql.h"
#include 

class pre_statement
{
public:
	pre_statement();
	~pre_statement();

	int init(MYSQL* mysql, string& sql);
	int set_param_bind(int index, int& value);
	int set_param_bind(int index, string& value);
	int set_param_bind(int index, MYSQL_TIME& value);
	int execute();

	int query();
	int set_param_result(int index, enum_field_types type, char* buffer, unsigned long buffer_length, unsigned long	*length);
	int get_result();
	int fetch_result();
	void free();

private:
	MYSQL_STMT* m_stmt;
	MYSQL_BIND* m_param_bind;
	MYSQL_BIND* m_result_bind;
	MYSQL_RES* m_result;
	unsigned long m_param_count;
	unsigned int m_result_count;
};

#endif

#include "pre_statement.h"

pre_statement::pre_statement()
{
	m_stmt = NULL;
	m_param_bind = NULL;
	m_result_bind = NULL;
	m_result = NULL;
	m_param_count = 0;
	m_result_count = 0;
}

pre_statement::~pre_statement()
{
	free();
}

int pre_statement::init(MYSQL* mysql, string& sql)
{
	m_stmt = mysql_stmt_init(mysql);
	if (!m_stmt)
	{
		return 1;
	}
	if (mysql_stmt_prepare(m_stmt, sql.c_str(), sql.size()))
	{
		return 1;
	}
	m_param_count = mysql_stmt_param_count(m_stmt);
	if (m_param_count > 0)
	{
		m_param_bind = new MYSQL_BIND[m_param_count];
		if (!m_param_bind)
		{
			return 1;
		}
		memset(m_param_bind, 0, sizeof(MYSQL_BIND)*m_param_count);
	}
	return 0;
}

int pre_statement::set_param_bind(int index, int& value)
{
	if (index >= m_param_count)
	{
		perror("索引超出总数！\n");
		return 1;
	}
	m_param_bind[index].buffer_type = MYSQL_TYPE_LONG;
	m_param_bind[index].buffer = &value;
	return 0;
}

int pre_statement::set_param_bind(int index, string& value)
{
	if (index >= m_param_count)
	{
		perror("索引超出总数！\n");
		return 1;
	}
	m_param_bind[index].buffer_type = MYSQL_TYPE_STRING;
	m_param_bind[index].buffer = (void*)(value.c_str());
	m_param_bind[index].buffer_length = value.size();
	return 0;
}

int pre_statement::set_param_bind(int index, MYSQL_TIME& value)
{
	if (index >= m_param_count)
	{
		perror("索引超出总数！\n");
		return 1;
	}
	m_param_bind[index].buffer_type = MYSQL_TYPE_TIMESTAMP;
	m_param_bind[index].buffer = &value;
	m_param_bind[index].buffer_length = sizeof(value);
	return 0;
}

int pre_statement::set_param_result(int index, enum_field_types type, char* buffer, unsigned long buffer_length, unsigned long	*length)
{
	if (index >= m_result_count)
	{
		perror("索引超出总数！\n");
		return 1;
	}
	m_result_bind[index].buffer_type = type;
	m_result_bind[index].buffer = buffer;
	m_result_bind[index].buffer_length = buffer_length;
	m_result_bind[index].length = length;
	return 0;
}

int pre_statement::execute()
{
	if (!m_stmt)
	{
		return 1;
	}
	if (mysql_stmt_bind_param(m_stmt, m_param_bind))
	{
		//mysql_stmt_errno(m_stmt);
		return 1;
	}
	if (mysql_stmt_execute(m_stmt))
	{
		//mysql_stmt_errno(m_stmt);
		return 1;
	}
	if (0 == mysql_stmt_affected_rows(m_stmt))
	{
		perror("更新失败没有改变！\n");
		return 1;
	}
	return 0;
}

int pre_statement::query()
{
	if (!m_stmt)
	{
		return 1;
	}
	if (mysql_stmt_bind_param(m_stmt, m_param_bind))
	{
		//mysql_stmt_errno(m_stmt);
		return 1;
	}
	m_result = mysql_stmt_result_metadata(m_stmt);
	if (NULL == m_result)
	{
		//mysql_stmt_errno(m_stmt);
		return 1;
	}
	else
	{
		m_result_count = mysql_num_fields(m_result);
		m_result_bind = new MYSQL_BIND[m_result_count];
		if (!m_result_bind)
		{
			return 1;
		}
		memset(m_result_bind, 0, sizeof(MYSQL_BIND)*m_result_count);
	}
	if (mysql_stmt_execute(m_stmt))
	{
		//mysql_stmt_errno(m_stmt);
		return 1;
	}
	return 0;
}

int pre_statement::get_result()
{
	if (mysql_stmt_bind_result(m_stmt, m_result_bind))
	{
		return 1;
	}
	if (mysql_stmt_store_result(m_stmt))
	{
		return 1;
	}
	return 0;
}

int pre_statement::fetch_result()
{
	if (!mysql_stmt_fetch(m_stmt))
	{
		return 0;
	}
	else
	{
		return 1;
	}
}

void pre_statement::free()
{
	if (m_stmt)
	{
		mysql_stmt_close(m_stmt);
		m_stmt = NULL;
	}
	if (m_param_bind)
	{
		delete[]m_param_bind;
		m_param_bind = NULL;
	}
	if (m_result_bind)
	{
		delete[]m_result_bind;
		m_result_bind = NULL;
	}
	if (NULL != m_result)
	{
		mysql_free_result(m_result);
		m_result = NULL;
	}
	m_param_count = 0;
	m_result_count = 0;
}

使用步骤说明：

1. init是将SQL语句和MySQL连接实例绑定在一起的，并且检测sql语句中含有多少个“？”，然后对应的创建bind数组，后面对数组内容赋值，就相当于对每个“？”赋值。

2. set_param_bind就是对SQL语句中的问号进行赋值，第一个索引index为0，和数组下标规则一样。

3. 执行execute就是执行SQL语句，先是把之前赋值了的bind带入到SQL语句中，然后execute执行，最后会检测是否对数据库行数造成了影响。

4. 如果此时SQL语句不是增删改，而是查，那么我们就不是步骤3调用execute了而是调用query，也是先把之前赋值了的bind带入到SQL语句中，然后metadata会计算这个查询语句得到的结果集的一个元数据（不带数据的只是结果集的属性列表），我们通过这个元数据要计算结果集列的数目，所以就num_fields。

5. 为结果集绑定bind，使用set_param_result，这里的buffer通过后面的执行，会得到列值。

6. 执行get_result获取结果集。

7. 执行fetch_result对结果集逐行来进行获取。

8. 最后关闭预处理语句，释放bind的内存，释放结果集。