http://jackxiang.com/index.php zh-cn http://jackxiang.com/post// jack <xdy108@126.com> Fri, 14 Nov 2014 06:09:56 +0000 http://jackxiang.com/post// 一、看一个简单的例子（学习其用static字符串数组和指针的返回判断这块值得学习并记住）：
#include <curl/curl.h> #include <stdio.h> #include <string.h> CURL *curl; CURLcode res; size_t write_data(void *ptr, size_t size, size_t nmemb, void *stream) {     if (strlen((char *)stream) + strlen((char *)ptr) > 999999) return 0;     strcat(stream, (char *)ptr);     return size*nmemb; } char *down_file(char *filename) {     static char str[10000000];     strcpy(str,"");     //return “”;     curl_easy_setopt(curl, CURLOPT_URL, filename); //设置下载地址     curl_easy_setopt(curl, CURLOPT_TIMEOUT, 3);//设置超时时间     curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);//设置写数据的函数     curl_easy_setopt(curl, CURLOPT_WRITEDATA, str);//设置写数据的变量     res = curl_easy_perform(curl);//执行下载     str[9999999] = '\0';     if(CURLE_OK != res) return NULL;//判断是否下载成功     return str; } int main() {     char url[200];     curl = curl_easy_init();//对curl进行初始化     char *result;     while(fgets(url, 200, stdin)){         result = down_file(url);         if (result) puts(result);         else puts("Get Error!");         printf("\nPlease Input a url:");     }     curl_easy_cleanup(curl);//释放curl资源     return 0; }

二、分为header和包体数据两个回调指针：
#if 1     curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, pc_method); #if (CURL_HEADER == 0)     curl_easy_setopt(curl, CURLOPT_HEADER, 1);         //下载数据包括HTTP头部, The default value for this parameter is 0.     curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, callback_get_head); //下载数据的回调函数     curl_easy_setopt(curl, CURLOPT_WRITEDATA, pc_ret);                                //下载数据的指针 #else     curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, callback_get_head); //头部数据的回调函数     curl_easy_setopt(curl, CURLOPT_HEADERDATA, pc_ret);                                //头部数据的指针 #endif     curl_easy_setopt(curl, CURLOPT_HTTPHEADER, http_headers);    //多行的HTTP头部 #endif

size_t callback_get_head(void *ptr, size_t size, size_t nmemb, void *userp) {     DBG("ptr = %s, userp = %sn", ptr, userp);     strcat(userp, ptr);     return size * nmemb; //必须返回这个大小, 否则只回调一次 }

整个代码如下：
/*------------------------------------------------------------------------------------------ 名称: http_cloud_curl_callbak.c 利用libcurl的API的回调机制实现云端通讯. http://curl.haxx.se/libcurl/c/curl_easy_setopt.html CURLOPT_HEADERFUNCTION, CURLOPT_HEADERDATA: 只处理HTTP头部数据,处理与下载数据回调的处理相同.     sina的股票接口因为无HTTP头部返回因此不能应用此. -------------------------------------------------------------------------------------------*/ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <curl/curl.h> #include <assert.h> #include "../http_cloud.h" #define CURL_HEADER (1)    //0=利用 CURLOPT_WRITEFUNCTION, 1=利用 CURLOPT_HEADERFUNCTION #define DBG printf #define CURL_DBG (0)    //1=开启curl的调试 //----------------------------------------------------------------------------------------- static void get_local_time(char *pc_str) {     time_t now;     struct tm *timenow;     assert(pc_str != NULL);     time(&now);     timenow = localtime(&now);     sprintf(pc_str, "%04d-%02d-%02dT%02d:%02d:%02d", timenow->tm_year+1900, timenow->tm_mon+1, timenow->tm_mday,                     timenow->tm_hour, timenow->tm_min, timenow->tm_sec); } size_t callback_get_head(void *ptr, size_t size, size_t nmemb, void *userp) {     DBG("ptr = %s, userp = %sn", ptr, userp);     strcat(userp, ptr);     return size * nmemb; //必须返回这个大小, 否则只回调一次 } static char connect_cloud(char *pc_ret, const char *host_addr, const int portno,         const char *pc_method, struct curl_slist *http_headers) {     CURL *curl;     CURLcode res = CURLE_GOT_NOTHING;   assert((pc_ret != NULL) && (host_addr != NULL) && (http_headers != NULL) && (pc_method != NULL));   //curl_global_init(CURL_GLOBAL_DEFAULT);   curl = curl_easy_init();   if (!curl)    {       fprintf(stderr, "--- curl init Error!n");       return 0;   }   curl_easy_setopt(curl, CURLOPT_URL, host_addr);   curl_easy_setopt(curl, CURL_HTTP_VERSION_1_1, 1L);    //HTTP 1.1   curl_easy_setopt(curl, CURLOPT_TIMEOUT, 3);     //设置超时, 单位为秒     //curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1);     //屏蔽其它信号, makes libcurl NOT ask the system to ignore SIGPIPE signals #if (CURL_DBG == 1)   curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);    //调试用: 显示交互明细,     //curl_easy_setopt(curl, CURLOPT_HEADER, 1L);    //调试用: 只显示头行的返回 #endif #if 1     curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, pc_method); #if (CURL_HEADER == 0)     curl_easy_setopt(curl, CURLOPT_HEADER, 1);         //下载数据包括HTTP头部, The default value for this parameter is 0.     curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, callback_get_head); //下载数据的回调函数     curl_easy_setopt(curl, CURLOPT_WRITEDATA, pc_ret);                                //下载数据的指针 #else     curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, callback_get_head); //头部数据的回调函数     curl_easy_setopt(curl, CURLOPT_HEADERDATA, pc_ret);                                //头部数据的指针 #endif     curl_easy_setopt(curl, CURLOPT_HTTPHEADER, http_headers);    //多行的HTTP头部 #endif   res = curl_easy_perform(curl);   if(res != CURLE_OK)       fprintf(stderr, "curl_easy_perform() failed: %sn", curl_easy_strerror(res));     curl_easy_cleanup(curl);   return 1; } #if (YEELINK == 1) int yeelink_create_data(const int device_id, const int sensor_id, const float device_value) {     char pc_ret[500], request[1024], pc_json[100], pc_time[30], pc_host_file[100], pc_header[100], pc_url[200], ret;     int len;     sprintf(pc_host_file, "v1.0/device/%d/sensor/%d/datapoints", device_id, sensor_id);     sprintf(pc_header, "U-ApiKey: %s", YEELINK_API_KEY);     get_local_time(pc_time);     sprintf(pc_json, "{"timestamp":"%s","value":%.2f}", pc_time, device_value);     len = strlen(pc_json);     //sprintf(request, "POST /%s HTTP/1.1rnHost: %srnAccept: */*rn%srnContent-Length: %drnContent-Type: application/x-www-form-urlencodedrnConnection: Closernrn%srn",     //    pc_host_file, YEELINK_HOST, pc_header, len, pc_json);     //DBG("request = %sn", request);     //组织请求头部, 自动末尾添加'rn'     struct curl_slist *http_headers = NULL;     //sprintf(request, "POST /%s HTTP/1.1", pc_host_file);     //http_headers = curl_slist_append(http_headers, request);    //此部分在url中体现     sprintf(request, "Host: %s", YEELINK_HOST);     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "%s", pc_header);     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "%s", "Accept: */*");     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "Content-Length: %d", len);     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "%s", "Content-Type: application/x-www-form-urlencoded");     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "%s", "Connection: Close");     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "rn%s", pc_json);     http_headers = curl_slist_append(http_headers, request); #if 0     struct curl_slist *tmp = http_headers;     printf("HTTP request = ");     while(tmp) {         printf("%sn", tmp->data);         tmp = tmp->next;     } #endif     //发送请求, 再判断返回值     //url = api.yeelink.net/v1.0/device/391/sensor/497/datapoints     sprintf(pc_url, "%s/%s", YEELINK_HOST, pc_host_file);     ret = connect_cloud(pc_ret, pc_url, YEELINK_PORT, HTTP_POST, http_headers);     //释放 http_headers资源     curl_slist_free_all(http_headers);     DBG("yeelini ret = %sn", pc_ret);     return(ret); } #endif #if (LEWEI50 == 1) //curl --request POST http://www.lewei50.com/api/V1/Gateway/UpdateSensors/01 --data "[{"Name":"T1","Value":"23.08"}]" --header "userkey:36be8ff22f794f1e8a0bee3336eef237" int lewei50_create_data(const char *device_id, const float device_value) {     char pc_ret[500], request[1024], pc_json[100], pc_header[100], pc_url[200], *pc_data, ret;     int len;     assert(device_id != NULL);     sprintf(pc_header, "userkey: %s", LEWEI50_USER_KEY);     sprintf(pc_json, "[{"Name":"%s","Value":"%.2f"}]", device_id, device_value);     len = strlen(pc_json);     //sprintf(request, "POST /%s HTTP/1.1rnHost: %srnAccept: */*rn%srnContent-Length: %drnContent-Type: application/x-www-form-urlencodedrnConnection: Closernrn%srn",     //    LEWEI50_HOST_FILE, LEWEI50_HOST, pc_header, len, pc_json);     //DBG("request = %sn", request);     //组织请求头部, 自动末尾添加'rn'     struct curl_slist *http_headers = NULL;     //sprintf(request, "POST /%s HTTP/1.1", pc_host_file);     //http_headers = curl_slist_append(http_headers, request);    //此部分在url中体现     sprintf(request, "Host: %s", LEWEI50_HOST);     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "%s", pc_header);     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "%s", "Accept: */*");     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "Content-Length: %d", len);     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "%s", "Content-Type: application/x-www-form-urlencoded");     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "%s", "Connection: Close");     http_headers = curl_slist_append(http_headers, request);     sprintf(request, "rn%s", pc_json);     http_headers = curl_slist_append(http_headers, request);     //发送请求, 再判断返回值     //url = www.lewei50.com/api/V1/gateway/UpdateSensors/01     sprintf(pc_url, "%s/%s", LEWEI50_HOST, LEWEI50_HOST_FILE);     ret = connect_cloud(pc_ret, pc_url, LEWEI50_PORT, HTTP_POST, http_headers);     //释放 http_headers资源     curl_slist_free_all(http_headers);     //{"Successful":true,"Message":"Successful. "}, 模式不同此返回数据的位置也不同.     DBG("lewei50 ret = %sn", pc_ret);     ret = 0;     pc_data = strstr(pc_ret, HTTP_RET_OK);     if (pc_data) {         pc_data += strlen(HTTP_RET_OK);         //只返回最后的 json数据         pc_data = strstr(pc_data, "rnrn");         if (pc_data) {             pc_data += 4;             ret = 1;             DBG("lewei50 data = %sn", pc_data);         }     }     return(ret); } #endif //------------------------------------------------------------------- int main(void) {     float f_value = 15.02;     int i_tmp;     time_t t;   srand((unsigned)time(&t));    //初始化随机种子, 否则随机数不随机     i_tmp = rand();     i_tmp -= (i_tmp >> 4 << 4);   f_value += i_tmp; #if (YEELINK == 1)     yeelink_create_data(YEELINK_DEVICE_ID, YEELINK_SENSOR_ID, f_value); #endif #if (LEWEI50 == 1)     lewei50_create_data(LEWEI50_DEVICE_ID, f_value); #endif     return 1; }
From:
http://www.ithao123.cn/content-1085192.html

curl连接超时的问题:
CURLOPT_TIMEOUT  设置cURL允许执行的最长秒数。  
CURLOPT_TIMEOUT_MS  设置cURL允许执行的最长毫秒数。
CURLOPT_CONNECTTIMEOUT  在发起连接前等待的时间，如果设置为0，则无限等待。  
CURLOPT_CONNECTTIMEOUT_MS  尝试连接等待的时间，以毫秒为单位。如果设置为0，则无限等待。

CURLOPT_CONNECTTIMEOUT 与 CURLOPT_CONNECTTIMEOUT_MS 类似,可以理解成等待连接成功创建的时间.
来自：http://blog.chinaunix.net/uid-2270658-id-302245.html
超时这一块还应该注意在不同的curl里存在毫秒，而上线后可能curl版本较低不支持毫秒，于是出现没有发出请求的问题：
来自：http://www.vimer.cn/2012/01/%E5%85%B3%E4%BA%8Elibcurl%E4%B8%8D%E5%8F%91%E5%8C%85%E7%9A%84bug%E5%AE%9A%E4%BD%8D.html

使用libcurl库可以实现HTTP和FTP的请求，以前对http协议进行过学习，但一直无法很好的解决阻塞问题，认识了libcurl后方觉相见恨晚，因为http阻塞的问题已经困扰了我两年了。
虽然编译出来的libcurl.lib足有700多K，但libcurl库的使用却很简单，只有熟悉curl_easy_setopt这个函数就可以了。该函数的作用是设置请求的相关参数来让curl构造协议头或返回指定的数据。
//返回HTTP协议头
curl_easy_setopt( curl, CURLOPT_HEADER, 1 );
//超时设置（单位：秒），如果在指定时间内没数据可接收则超时
curl_easy_setopt( curl, CURLOPT_TIMEOUT, 3 );
//连接超时，不过只适用于Unix系统，Windows系统应该就是使用CURLOPT_TIMEOUT
curl_easy_setopt( curl, CONNECTTIMEOUT, 3 );
//设置请求Cookie
curl_easy_setopt( curl, CURLOPT_COOKIE, cookie );
//返回Cookie
curl_easy_setopt( curl, CURLOPT_COOKIEJAR, cookie );

来自：http://blog.chinaunix.net/uid-2270658-id-247815.html

通常情况下，一般很少使用C语言来直接上传文件，但是遇到使用C语言编程实现文件上传时，该怎么做呢？

      借助开源的libcurl库，我们可以容易地实现这个功能。Libcurl是一个免费易用的客户端URL传输库，主要功能是用不同的协议连接和沟通不同的服务器，libcurl当前支持DICT, FILE, FTP, FTPS, Gopher, HTTP, HTTPS, IMAP,IMAPS, LDAP, LDAPS, POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, Telnet andTFTP。libcurl同样支持HTTPS证书授权，HTTP POST, HTTP PUT, FTP 上传, HTTP基本表单上传，代理，cookies,和用户认证等。下面借鉴libcurl官网的例子完成简单的文件上传。

模拟要实现的文件上传FORM：

<form action="fileUpload.action" method="post" enctype="multipart/form-data">           File:<input type="file" name="sendfile" /><br>           FileName:<input type="text" name="filename" /><br>           <input type="submit" name="submit" value="Submit" />   </form>  
      其中，fileUpload.action为文件处理文件上传的接口，根据实际需要配置，这里只是一个例子。
      C语言HTTP上传文件的代码如下：

#include <stdio.h>   #include <string.h>   #include <curl/curl.h>      int main(int argc, char *argv[])   {     CURL *curl;     CURLcode res;        struct curl_httppost *formpost=NULL;     struct curl_httppost *lastptr=NULL;     struct curl_slist *headerlist=NULL;     static const char buf[] = "Expect:";        curl_global_init(CURL_GLOBAL_ALL);        /* Fill in the file upload field */     curl_formadd(&formpost,                  &lastptr,                  CURLFORM_COPYNAME, "sendfile",                  CURLFORM_FILE, "D:\\sign.txt",                  CURLFORM_END);        /* Fill in the filename field */     curl_formadd(&formpost,                  &lastptr,                  CURLFORM_COPYNAME, "filename",                  CURLFORM_COPYCONTENTS, "sign.txt",                  CURLFORM_END);        /* Fill in the submit field too, even if this is rarely needed */     curl_formadd(&formpost,                  &lastptr,                  CURLFORM_COPYNAME, "submit",                  CURLFORM_COPYCONTENTS, "Submit",                  CURLFORM_END);        curl = curl_easy_init();     /* initalize custom header list (stating that Expect: 100-continue is not      wanted */     headerlist = curl_slist_append(headerlist, buf);     if(curl) {       /* what URL that receives this POST */   <span style="white-space:pre">  </span>curl_easy_setopt(curl, CURLOPT_URL, "http://localhost:8080/fileUpload.action");       if ( (argc == 2) && (!strcmp(argv[1], "noexpectheader")) )         /* only disable 100-continue header if explicitly requested */         curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headerlist);       curl_easy_setopt(curl, CURLOPT_HTTPPOST, formpost);          /* Perform the request, res will get the return code */       res = curl_easy_perform(curl);       /* Check for errors */       if(res != CURLE_OK)         fprintf(stderr, "curl_easy_perform() failed: %s\n",                 curl_easy_strerror(res));          /* always cleanup */       curl_easy_cleanup(curl);          /* then cleanup the formpost chain */       curl_formfree(formpost);       /* free slist */       curl_slist_free_all (headerlist);     }     return 0;   }  
代码经过测试，可以使用，但是需要提前配置好Libcur库，以及编译环境，这个自行google。代码很粗糙，功能很简单，只是起个抛砖引玉的作用，希望能对大家有所帮助。
来自：http://blog.csdn.net/sxwyf248/article/details/7984776
VC2013下，使用curl：
http://www.tuicool.com/articles/A73ARr
较细：http://blog.csdn.net/mjpassion/article/details/6290912
Visual2012：http://www.howzhi.com/course/3387/lesson/43112
参考：http://www.cppblog.com/len/archive/2008/06/21/54229.html
使用libcurl模拟form表单上传的问题：
http://bbs.csdn.net/topics/390817077
在C语言程序中使用cURL库（libcurl）：
http://demon.tw/programming/c-libcurl.html ]]> http://jackxiang.com/post//#blogcomment <user@domain.com> Thu, 01 Jan 1970 00:00:00 +0000 http://jackxiang.com/post//#blogcomment