c - 如何在C中使用curl获取响应值

Question

在 C 中使用curl 执行 http post 后，我​​在获取响应值时遇到困难。

我收到如下回复:

POST /xxxx HTTP/1.1
Host: xxxx.net
Accept: */*
Content-Length: 271
Content-Type: application/x-www-form-urlencoded

HTTP/1.1 200 OK
Content-Type: text/xml
Date: Tue, 18 Nov 2014 13:49:31 GMT
Server: Null
Content-Length: 106
Connection: keep-alive

<?xml version="1.0" encoding="UTF-8"?>
<rsp stat="fail">
<err code="100" msg="Invalid_Parameter"/>
</rsp>

如何使用curl获取xml响应值？

我使用curl_easy_perform来处理http post。

我看过帮助文档，但只能找到CURLINFO_HTTP_CODE和CURLINFO_CONTENT_TYPE。 但它与 xml 响应值无关。我应该使用什么样的curl_easy_getinfo参数？

Answer 1

默认情况下，响应数据会写入 STDOUT。要更改此设置，请使用 curl_easy_setopt(CURLOPT_WRITEFUNCTION) 和 curl_easy_setopt(CURLOPT_WRITEDATA) 来使用自定义写入函数和内存缓冲区。文档中提供了此技术的示例:

http://curl.haxx.se/libcurl/c/getinmemory.html

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2013, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at http://curl.haxx.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ***************************************************************************/ 
/* Example source code to show how the callback function can be used to
 * download data into a chunk of memory instead of storing it in a file.
 */ 

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

#include <curl/curl.h>

struct MemoryStruct {
  char *memory;
  size_t size;
};


static size_t
WriteMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp)
{
  size_t realsize = size * nmemb;
  struct MemoryStruct *mem = (struct MemoryStruct *)userp;

  mem->memory = realloc(mem->memory, mem->size + realsize + 1);
  if(mem->memory == NULL) {
    /* out of memory! */ 
    printf("not enough memory (realloc returned NULL)\n");
    return 0;
  }

  memcpy(&(mem->memory[mem->size]), contents, realsize);
  mem->size += realsize;
  mem->memory[mem->size] = 0;

  return realsize;
}


int main(void)
{
  CURL *curl_handle;
  CURLcode res;

  struct MemoryStruct chunk;

  chunk.memory = malloc(1);  /* will be grown as needed by the realloc above */ 
  chunk.size = 0;    /* no data at this point */ 

  curl_global_init(CURL_GLOBAL_ALL);

  /* init the curl session */ 
  curl_handle = curl_easy_init();

  /* specify URL to get */ 
  curl_easy_setopt(curl_handle, CURLOPT_URL, "http://www.example.com/");

  /* send all data to this function  */ 
  curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);

  /* we pass our 'chunk' struct to the callback function */ 
  curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, (void *)&chunk);

  /* some servers don't like requests that are made without a user-agent
     field, so we provide one */ 
  curl_easy_setopt(curl_handle, CURLOPT_USERAGENT, "libcurl-agent/1.0");

  /* get it! */ 
  res = curl_easy_perform(curl_handle);

  /* check for errors */ 
  if(res != CURLE_OK) {
    fprintf(stderr, "curl_easy_perform() failed: %s\n",
            curl_easy_strerror(res));
  }
  else {
    /*
     * Now, our chunk.memory points to a memory block that is chunk.size
     * bytes big and contains the remote file.
     *
     * Do something nice with it!
     */ 

    printf("%lu bytes retrieved\n", (long)chunk.size);
  }

  /* cleanup curl stuff */ 
  curl_easy_cleanup(curl_handle);

  if(chunk.memory)
    free(chunk.memory);

  /* we're done with libcurl, so clean it up */ 
  curl_global_cleanup();

  return 0;
}