MySQL返回来的值都是字符串类型，还原每个字段【转载】

转载自https://chuanke.baidu.com/v4509752-209102-1284621.html C语言C++学习指南（数据库篇）MySQL与SQLite

AfMysql.h

#ifndef _AF_MYSQL_H
#define _AF_MYSQL_H

/* AfMysql
     用于将MySQL的字段值转成相应的类型

    
     版本：2015-12-20
     官网：http://afanihao.cn   C/C++学习指南(MySQL篇)
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <string>
using std::string;

class AfMysql
{
public:
    // 日期时间类型
    struct Date
    {
        Date():year(2000),month(1), day(1){}
        int year,month,day;
    };
    struct Time
    {
        Time():hour(0),minute(0), second(0){}
        int hour,minute,second;
    };
    struct DateTime
    {
        DateTime(): year(2000), month(1), day(1), hour(0), minute(0), second(0) {}
        int year,month,day;
        int hour,minute,second;
    };

    // 字符串类型
    typedef string  String;
    typedef int Int;
    typedef long long BigInt;

public:
    static Int AsInt(const char* field, int length)
    {
        if(field==NULL) return 0;
        return atoi(field);        
    }

    static BigInt AsBigInt(const char* field, int length)
    {
        if(field==NULL) return 0;

        long long val;
#ifdef _WIN32
        sscanf(field, "%I64d", &val);
#else
#endif
        return val;
    }

    // 时间类型
    static Date AsDate(const char* field, int length)
    {
        Date val;
        if(field==NULL) return val;

        sscanf(field, "%d-%d-%d", &val.year, &val.month, &val.day);
        return val;
    }
    static Time AsTime(const char* field, int length)
    {
        Time val;
        if(field==NULL) return val;

        sscanf(field, "%d:%d:%d", &val.hour, &val.minute, &val.second);
        return val;
    }

    static DateTime AsDateTime(const char* field, int length)
    {
        DateTime val;
        if(field==NULL) return val;

        sscanf(field,  "%d-%d-%d %d:%d:%d", 
            &val.year, &val.month, &val.day,
            &val.hour, &val.minute, &val.second);
        return val;
    }

    static String AsString(const char* field, int length)
    {
        if(field==NULL) return "";

        String val = field;
        return val;
    }

};





#endif

main.cpp

#include <stdio.h>
#include <stdlib.h>

#include "AfMysql.h"

// MySQL support on Windows
#include <WinSock2.h>
#include <mysql.h>
#pragma comment(lib, "libmysql")


int my_select(MYSQL* conn)
{
    // SQL语句，末尾不加分号。每次只执行一条SQL语句。
    const char* sql = "SELECT * FROM student"; 
    int ret = mysql_query(conn, sql);
    if(ret != 0)
    {
        printf("error: %s 
", mysql_error(conn));
        return -1;
    }

    MYSQL_RES * result = mysql_store_result(conn);
    if(result == NULL)
    {
        //printf("error(%d): %s 
", mysql_errno(conn), mysql_error(conn));
    }
    else
    {
        // how many rows
        my_ulonglong num_rows = mysql_num_rows(result);
        printf("got %d rows: 
", (int)num_rows);

        // number of fields for each row
        unsigned int num_fields = mysql_num_fields(result);
        printf("number of fields: %d 
", (int)num_fields);

        // fetch the rows
        MYSQL_ROW row;
        while ((row = mysql_fetch_row(result)))
        {
            unsigned long *lengths = mysql_fetch_lengths(result);
            for(int i = 0; i < num_fields; i++)
            {
                char* field = row[i]; // can be a NULL value
                unsigned int field_length = lengths[i]; // the data length

                //printf("     column[%d], length[%d] , data[%s] 
",
                //    i, field_length, field ? field : "null");
                // 处理每个字段
                if(i==0)
                {
                    AfMysql::Int val = AfMysql::AsInt(field, field_length);
                    printf("id: %d 
", val);
                }
                if(i==1)
                {
                    AfMysql::String val = AfMysql::AsString(field, field_length);
                    printf("name: %s 
", val.c_str());
                }
                if(i==2)
                {
                    AfMysql::Date val = AfMysql::AsDate(field, field_length);
                    printf("date: %d-%d-%d
", val.year, val.month, val.day);
                }
                if(i==3)
                {
                    AfMysql::String val = AfMysql::AsString(field, field_length);
                    printf("cellphone: %s 
", val.c_str());
                }
            }
            printf("
");
        }

        // release the memory
        mysql_free_result(result) ;
    }

    return 0;
}

int main()
{
    long long val;
    sscanf("102388982430234", "%I64d", &val);

    if (mysql_library_init(0, NULL, NULL))
    {
        printf("could not initialize MySQL library
");
        return -1;
    }

    // 连接服务器
    MYSQL conn;
    mysql_init(&conn);

    MYSQL* ret = mysql_real_connect(&conn,
        "127.0.0.1","root","123456","example"
        ,0,NULL,0);
    if (!ret)
    {
        printf("Failed to connect to database:  %s
",
            mysql_error(&conn));
    }

    my_select(&conn);

    // 关闭连接
    mysql_close(&conn);

    mysql_library_end();
    return 0;
}