C|本地时间自动同步网络时间

很多情况导致电脑开机后总是从00:00开始，如主板CMOS电池供电不足。时间不对有时会导致网络浏览提示日期没有更新而不能正常访问。虽然Windows系统也有同步到internet时间的操作界面，需要多次点击。但如果是旧电脑，每次开机都要去更新这个时间，非常繁琐。所以，可以写一个自动将本地时间同步到网络时间的小程序。

1 C语言如何设置Windows平台的本地时间

1.1 C语言Windows时钟的结构体如下：

typedef struct _SYSTEMTIME {  
  WORD wYear;              /*年*/  
  WORD wMonth;             /*月*/  
  WORD wDayOfWeek;         /*星期  0-6  0-Sunday...*/  
  WORD wDay;               /*日*/  
  WORD wHour;              /*时*/  
  WORD wMinute;            /*分*/  
  WORD wSecond;            /*秒*/  
  WORD wMilliseconds;      /*微妙*/  
} SYSTEMTIME, *PSYSTEMTIME;

1.2 设置本地时间的API

windows.h提供的函数SetLocalTime()可以设置本地时间。

BOOL WINAPI SetLocalTime(  
  _In_  const SYSTEMTIME *lpSystemTime  
);

其参数就是上述的结构体指针。

_In_在visual C++中属于SAL批注，是为了编译系统在分析代码时发现缺陷用的。表示是一个输入参数。类似的还有_Out_。

2 获取某些网站页面返回的时间字符串

如以下站点

http://quan.suning.com/getSysTime.do

页面显示：

{"sysTime2":"2022-08-10 08:40:08","sysTime1":"20220810084008"}

通过socket套接字编程即可提取到该页面返回的字符串，如：

19,36,200-0,M], cache20.cn3603[43,0]

X-Cache: MISS TCP_MISS dirn:-2:-2

X-Swift-SaveTime: Wed, 10 Aug 2022 00:50:57 GMT

X-Swift-CacheTime: 0

Timing-Allow-Origin: *

EagleId: 708422a816600926577736154e

{"sysTime2":"2022-08-10 08:50:57","sysTime1":"20220810085057"}-cache,no-store,ma

x-age=0,s-maxage=0

Access-Control-Allow-Credentials: true

es-suning-dnsstr: quan.suning.com:tradema:default

Ali-Swift-Global-Savetime: 1660092657

Via: cache46.l2cn3036[8,10,200-0,M], cache79.l2cn3036[12,0], cache3.cn3603[…

3 提取需要的字符串

4 调用SetLocalTime()设置本地时间

code demo:

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include <string.h>
#pragma comment(lib, "ws2_32.lib")
/*
 * 国家授时中心 http://www.ntsc.ac.cn/
 * 获取网络时间的网站API
 * 苏宁 http://quan.suning.com/getSysTime.do 
 * 淘宝 http://api.m.taobao.com/rest/api3.do?api=mtop.common.getTimestamp
 * QQ   http://cgi.im.qq.com/cgi-bin/cgi_svrtime
**/

char* getTimeTxt(char *url);
int set_local_time(const char *timeStr);

int main() 
{
    char * time = getTimeTxt("quan.suning.com/getSysTime.do");
    if(time==NULL)
    {
        printf("返回的是乱字符串！\n");
        printf("3秒后自动关闭窗口……");
        Sleep(3000);
        exit(1);
    }
    printf("正在应用设置...\n");
    //strcpy(time,"20220807174237");
    //printf("%s\n",time);
    if(set_local_time(time)==0)
        printf("设置时间成功！\n\n");
    else
        printf("设置时间失败，可能是没有权限");
    printf("3秒后自动关闭窗口……");
    Sleep(3000);
    //getTimeTxt("api.mmuaa.com/gettime");
    //getchar();
    return 0;
}

char* getTimeTxt(char *url) 
{
    WSADATA WSAData= {0};
    if(WSAStartup(MAKEWORD(2,2), &WSAData)) {           // WSAStartup
        printf("WSA 失败!\n");
        return false;
    }

    SOCKET  sockfd;
    sockfd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP); // socket 

    char myurl[BUFSIZ];
    strcpy(myurl, url);
    
    char *pHost = 0;
    char GET[BUFSIZ];

    for (pHost = myurl; *pHost != '/' && *pHost != '\0'; ++pHost);  // ↓
    if ( (int)(pHost - myurl) == strlen(myurl) )
        strcpy(GET, "/");
    else
        strcpy(GET, pHost);
    *pHost = '\0';

    struct hostent *pURL;
    pURL = gethostbyname(myurl);
    struct sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = *((unsigned long*)pURL->h_addr);         // ↑
    addr.sin_port = htons(80);
    connect(sockfd,(SOCKADDR *)&addr,sizeof(addr));     // connecting
    printf("正在给网络API（%s）发送请求...\n",url);
    
    char header[BUFSIZ] = "";
    strcat(header, "GET ");
    strcat(header, GET);
    strcat(header, " HTTP/1.1\r\n");
    strcat(header, "HOST: ");
    strcat(header, myurl);
    strcat(header, "\r\nConnection: Close\r\n\r\n");
    send(sockfd, header, strlen(header), 0);            // sending

    printf("正在处理请求...\n");
    static char text[BUFSIZ*2];
    while ( recv(sockfd, text, BUFSIZ, 0) > 0);         // receiving
    closesocket(sockfd);
    WSACleanup();

    text[BUFSIZ*2-1] = '\0';
    if(strlen(text) == 0)
        printf("text is empty!\n");
    else
        printf("\n网络API（%s）返回字符串：\n%s\n",url,text);
   
    char* subStr = "sysTime1";                          // 文本处理
    char* str = strstr(text,subStr);
    if(str == NULL)
        return NULL;
    str = str + strlen(subStr) + 3; // "sysTime1":"20220807203344
    //printf("abc  123    %s\n",str);
    char *time = (char*)malloc(sizeof(char)*15);
    strncpy(time,str,14);
    time[14] = '\0';
    printf("\n成功获得时间:%s\n",time);
    return time;
}
/* 
 * @function : 设置Windows本地时间 
 * @in       : timeStr - 14字节时间字符串(such as 20150415093000) 
 * @return   : 0 - success 
 *            -1 - failure 
**/
int set_local_time(const char *timeStr)  
{  
    SYSTEMTIME system_time  = {0};  
    char year[4 + 1]        = {0};  
    char month[2 + 1]       = {0};  
    char day[2 + 1]         = {0};  
    char hour[2 + 1]        = {0};  
    char minute[2 + 1]      = {0};  
    char second[2 + 1]      = {0};  
    int index = 0;  
  
    strncpy(year,   timeStr + index, 4);  
    index += 4;  
    strncpy(month,  timeStr + index, 2);  
    index += 2;  
    strncpy(day,    timeStr + index, 2);  
    index += 2;  
    strncpy(hour,   timeStr + index, 2);  
    index += 2;  
    strncpy(minute, timeStr + index, 2);  
    index += 2;  
    strncpy(second, timeStr + index, 2);  
    index += 2;  
  
    GetLocalTime(&system_time);  
  
    system_time.wYear   = atoi(year);  
    system_time.wMonth  = atoi(month);  
    system_time.wDay    = atoi(day);  
    system_time.wHour   = atoi(hour);  
    system_time.wMinute = atoi(minute);  
    system_time.wSecond = atoi(second);  

    if (0 == SetLocalTime(&system_time))   
        return -1;      
    return 0;  
}

当然，以上小程序要手动运行才可以同步网络时间，要自动同步的话，可以通过”计划任务“自动运行。

以上代码没有考虑网络延迟的问题。在从服务器获取时间数据时，由于网络本身的不稳定性，一般会有时间上的延迟（几秒以内），这样一来，从服务器接收到的数据总早于真实时间。解决的办法是设定一个计时器，计算出本机从开始网络连接到接收完数据所耗费的时间dwDelay，然后加到 dwTime 上进行补偿。这样一来误差就可以控制在1秒以内。

以下网站返回的时间是豪秒数：

http://api.m.taobao.com/rest/api3.do?api=mtop.common.getTimestamp

页面显示：

{"api":"mtop.common.getTimestamp","v":"*","ret":["SUCCESS::接口调用成功"],"data":{"t":"1660091956996"}}

表示从1900.1.1至现在流逝的时间：

#include <stdio.h>
#include <time.h>

int main ()
{
    time_t timer;           // typedef long time_t
    struct tm y1900 = {0};
    double seconds;
    // 定义1900.1.1
    y1900.tm_hour   = 0;   
    y1900.tm_min    = 0; 
    y1900.tm_sec    = 0;
    y1900.tm_year   = 0; 
    y1900.tm_mon    = 0; 
    y1900.tm_mday   = 1;
    
    time(&timer);  /* get current time; same as: timer = time(NULL)  */
    
    seconds = difftime(timer,mktime(&y1900));
    
    printf ("lapsed %.f seconds since January 1, y1900 to now in the current timezone", seconds);
    getchar();
    return 0;
}
/*output:
lapsed 1660093185 seconds since January 1, y1900 to now in the current timezone
*/

localtime()可转换时间格式：

#include <stdio.h>
#include <time.h>
  // struct tm * localtime (const time_t * timer);
#if 0
struct tm {
        int tm_sec;     /* seconds after the minute - [0,59] */
        int tm_min;     /* minutes after the hour - [0,59] */
        int tm_hour;    /* hours since midnight - [0,23] */
        int tm_mday;    /* day of the month - [1,31] */
        int tm_mon;     /* months since January - [0,11] */
        int tm_year;    /* years since 1900 */
        int tm_wday;    /* days since Sunday - [0,6] */
        int tm_yday;    /* days since January 1 - [0,365] */
        int tm_isdst;   /* daylight savings time flag */
};
#endif
int main ()
{
    time_t rawtime;
    struct tm * timeinfo;
    
    time (&rawtime);
    timeinfo = localtime (&rawtime);
    printf ("Current local time and date: %s", asctime(timeinfo));
    getchar();
    return 0;
}
/*output:
Current local time and date: Wed Aug 10 09:06:33 2022
*/

ref

https://www.mmuaa.com/post/3281abd440aeb073.html

https://www.likecs.com/show-306240829.html

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