1.  利用 CURLOPT_WRITEFUNCTION 设置回调函数, 利用 CURLOPT_WRITEDATA 获取数据指针 

官网文档如下

CALLBACK OPTIONS

 

CURLOPT_WRITEFUNCTION

Pass a pointer to a function that matches the following prototype: size_t function( char *ptr, size_t size, size_t nmemb, void *userdata); This function gets called by libcurl as soon as there is data received that needs to be saved. The size of the data pointed to by ptr is size multiplied with nmemb, it will not be zero terminated. Return the number of bytes actually taken care of. If that amount differs from the amount passed to your function, it'll signal an error to the library. This will abort the transfer and return CURLE_WRITE_ERROR.

From 7.18.0, the function can return CURL_WRITEFUNC_PAUSE which then will cause writing to this connection to become paused. See  for further details.

This function may be called with zero bytes data if the transferred file is empty.

Set this option to NULL to get the internal default function. The internal default function will write the data to the FILE * given with .

Set the userdata argument with the  option.

The callback function will be passed as much data as possible in all invokes, but you cannot possibly make any assumptions. It may be one byte, it may be thousands. The maximum amount of body data that can be passed to the write callback is defined in the curl.h header file: CURL_MAX_WRITE_SIZE (the usual default is 16K). If you however have  set, which sends header data to the write callback, you can get up to CURL_MAX_HTTP_HEADER bytes of header data passed into it. This usually means 100K.

CURLOPT_WRITEDATA

Data pointer to pass to the file write function. If you use the  option, this is the pointer you'll get as input. If you don't use a callback, you must pass a 'FILE *' (cast to 'void *') as libcurl will pass this to fwrite() when writing data. By default, the value of this parameter is unspecified.

The internal  will write the data to the FILE * given with this option, or to stdout if this option hasn't been set.

If you're using libcurl as a win32 DLL, you MUST use the  if you set this option or you will experience crashes.

This option is also known with the older name CURLOPT_FILE, the name  was introduced in 7.9.7.

2. 完整代码如下:

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/*------------------------------------------------------------------------------------------
名称: http_sina_curl_callbak.c
功能: 利用libcurl的回调机制实现sina股票接口. http://curl.haxx.se/libcurl/c/curl_easy_setopt.html

http://hq.sinajs.cn/list=sz150013
http://hq.sinajs.cn/list=sh601318

#libcurl的调试信息
* About to connect() to hq.sinajs.cn port 80 (#0)
* Trying 219.142.78.242...
* connected
* Connected to hq.sinajs.cn (219.142.78.242) port 80 (#0)
> GET /list=sz150001 HTTP/1.1
Host: hq.sinajs.cn
Accept: * *

< HTTP/1.1 200 OK
< Cache-Control: no-cache
< Content-Length: 250
< Connection: Keep-Alive
< Content-Type: application/x-javascript; charset=GBK
<
* Connection #0 to host hq.sinajs.cn left intact
* Closing connection #0

#运行结果:
root@OpenWrt:/xutest# ./http_sina_stock
sz150001: dq = 0.724, jg = 0.730, jd = 0.722, jk = 0.729
sz150013: dq = 0.886, jg = 0.893, jd = 0.885, jk = 0.889
sz150100: dq = 0.981, jg = 0.982, jd = 0.979, jk = 0.980
sz150152: dq = 0.964, jg = 0.967, jd = 0.964, jk = 0.965
sz150018: dq = 0.958, jg = 0.960, jd = 0.957, jk = 0.960
root@OpenWrt:/xutest#
-------------------------------------------------------------------------------------------*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <curl/curl.h>
#include <assert.h>

#define HTTP_GET "GET"
#define HTTP_PUT "PUT"
#define HTTP_HEAD "HEAD"
#define HTTP_POST "POST"
#define HTTP_DELETE "DELETE"
#define HTTP_RET_OK "HTTP/1.1 200 OK\r\n"

#define SINA_HOST "hq.sinajs.cn"
#define SINA_PORT 80

#define ARRAY_COUNT(x) (sizeof(x) / sizeof(x[0]))

typedef struct {
    float price_dq;    //当前价, 取拼音的首字母
    float price_zs;    //昨收价
    float price_jk;    //今开价
    float price_jg;    //今高价
    float price_jd;    //今低价
} stock_info_t;

#define DBG //printf
#define CURL_DBG (0)    //1=开启curl的调试

//-----------------------------------------------------------------------------------------
static void delay_ms(int msec)
{
    struct timeval timeout;

    memset(&timeout, 0, sizeof(struct timeval));
    timeout.tv_sec    = msec / 1000;
    timeout.tv_usec    = (msec % 1000) * 1000;
    select(0, NULL, NULL, NULL, &timeout);
}

size_t callback_get_head(void *ptr, size_t size, size_t nmemb, void *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) && (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, 1L);     //屏蔽其它信号, makes libcurl NOT ask the system to ignore SIGPIPE signals
    curl_easy_setopt(curl, CURLOPT_HEADER, 1L);         //下载数据包括HTTP头部, The default value for this parameter is 0.
    //curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0);    //The default value for this parameter is 1

#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);

    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

    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: %s\n", curl_easy_strerror(res));

    curl_easy_cleanup(curl);

  return 1;
}

int sina_get_stock(char *pc_ret, const char *pc_stockid)
{
    char pc_url[200], ret;

    //组织请求头部, 自动末尾添加'\r\n'
    struct curl_slist *http_headers = NULL;
    http_headers = curl_slist_append(http_headers, "Accept: */*");
    //http_headers = curl_slist_append(http_headers, "Connection: Close");

    //发送请求, 再判断返回值
    //url = hq.sinajs.cn/list=sz150013
    sprintf(pc_url, "%s/list=%s", SINA_HOST, pc_stockid);
    ret = connect_cloud(pc_ret, pc_url, SINA_PORT, HTTP_GET, http_headers);
    //DBG("cloud ret = %s\n", pc_ret);

    //释放 http_headers资源
    curl_slist_free_all(http_headers);

    return(ret);
}

#if 0
/*字符串不同含义的数据用逗号隔开了，按照程序员的思路，顺序号从0开始。
0：”大秦铁路”，股票名字；
1：”27.55″，今日开盘价；
2：”27.25″，昨日收盘价；
3：”26.91″，当前价格；
4：”27.55″，今日最高价；
5：”26.20″，今日最低价；
6：”26.91″，竞买价，即“买一”报价；
7：”26.92″，竞卖价，即“卖一”报价；
8：”22114263″，成交的股票数，由于股票交易以一百股为基本单位，所以在使用时，通常把该值除以一百；
9：”589824680″，成交金额，单位为“元”，为了一目了然，通常以“万元”为成交金额的单位，所以通常把该值除以一万；
10：”4695″，“买一”申请4695股，即47手；
11：”26.91″，“买一”报价；
12：”57590″，“买二”
13：”26.90″，“买二”
14：”14700″，“买三”
15：”26.89″，“买三”
16：”14300″，“买四”
17：”26.88″，“买四”
18：”15100″，“买五”
19：”26.87″，“买五”
20：”3100″，“卖一”申报3100股，即31手；
21：”26.92″，“卖一”报价
(22, 23), (24, 25), (26,27), (28, 29)分别为“卖二”至“卖四的情况”
30：”2008-01-11″，日期；
31：”15:05:32″，时间；*/
#endif

void stock_parse(stock_info_t *stock, const char *pc_data)
{
    char *pc_str, *pc_str1;
    int i;

    assert((stock != NULL) &&(pc_data != NULL));

    //DBG("data = %s\n", pc_data);
    pc_str = strstr(pc_data, HTTP_RET_OK);
    if (pc_str) {
        pc_str += strlen(HTTP_RET_OK);

        pc_str = strstr(pc_str, "\r\n\r\n");
        pc_str += 4;
        DBG("valid str = %s\n", pc_str);

        //解析数据, var hq_str_sz150013="???B,0.899,0.906,0.897,0.903,0.895,0.897,0.898,9739979,8751058.780,2200,0.897,143548,0.896,572900,0.895,625300,0.894,167300,0.893,9800,0.898,60000,0.899,362300,0.900,162500,0.901,217000,0.902,2013-11-06,10:38:44,00";
        pc_str = strchr(pc_str, ',');
        pc_str ++;

        for (i=0; i<5; i++) {
            pc_str1 = strchr(pc_str, ',');
            if (pc_str1) {
                *pc_str1 = '\0';
                switch(i) {
                    case 0: stock->price_jk = atof(pc_str); break;    //今开
                    case 1: stock->price_zs = atof(pc_str); break;    //昨收
                    case 2: stock->price_dq = atof(pc_str); break;    //当前
                    case 3: stock->price_jg = atof(pc_str); break;    //今高
                    case 4: stock->price_jd = atof(pc_str); break;    //今低
                }

                pc_str = pc_str1 + 1;    //指向下个有效数据
            }
            else break;
        }
    }
}

//-------------------------------------------------------------------------------
int main(void)
{
    char pc_ret[1000];
    int i, max;
    stock_info_t stock;

    char *stock_array[] = {             "sz150001", "sz150013", "sz150100", "sz150152", "sz150018"};    //改成自己的
    max = ARRAY_COUNT(stock_array);

    for(i=0; i<max; i++) {
        memset(pc_ret, 0x00, sizeof(pc_ret));
        sina_get_stock(pc_ret, stock_array[i]);
        DBG("sina ret OK = %s\n", pc_ret);
        stock_parse(&stock, pc_ret);
        printf("%s: dq = %.3f, jg = %.3f, jd = %.3f, jk = %.3f\n",
                stock_array[i], stock.price_dq, stock.price_jg, stock.price_jd ,stock.price_jk);
    }

    return 1;
}

3. Makefile: 

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OPENWRT = 1

ifeq ($(OPENWRT), 1)
    CC = ~/OpenWrt-SDK-ar71xx-for-linux-i486-gcc-4.6-linaro_uClibc-0.9.33.2/staging_dir/toolchain-mips_r2_gcc-4.6-linaro_uClibc-0.9.33.2/bin/mips-openwrt-linux-gcc
    CFLAGS += -I ~/openwrt-lib/include -L ~/openwrt-lib/lib
    LFLAGS += -lcurl -lcrypto -lz -lssl

else
    CC = gcc
    LFLAGS += -lcurl
endif

CFLAGS += -Wall -O2
#CFLAGS += -g

#可执行文件名和相关的obj文件
APP_BINARY = http_sina_stock
SRCS += http_sina_curl_callback.c
OBJS = $(SRCS:.c=.o)

all: APP_FILE

APP_FILE: $(OBJS)
    $(CC) $(CFLAGS) $(OBJS) -o $(APP_BINARY) $(LFLAGS)

.PHONY: clean
clean:
    @echo "cleanning project"
    $(RM) *.a $(OBJS) *~ *.so *.lo $(APP_BINARY)
    @echo "clean completed"

4. openwrt下运行结果如下

root@OpenWrt:/xutest# ./http_sina_stock

sz150001: dq = 0.724, jg = 0.730, jd = 0.722, jk = 0.729

sz150013: dq = 0.886, jg = 0.893, jd = 0.885, jk = 0.889

sz150100: dq = 0.981, jg = 0.982, jd = 0.979, jk = 0.980

sz150152: dq = 0.964, jg = 0.967, jd = 0.964, jk = 0.965

sz150018: dq = 0.958, jg = 0.960, jd = 0.957, jk = 0.960

root@OpenWrt:/xutest#