从Cpp中的URL下载时获取空CSV [英] Getting an empty CSV when downloading from URL in Cpp

问题描述

我的目标是使用Cpp从特定的URL获取CSV或XLS。

打开以下链接时

  http://www.centrodeinformacao.ren.pt/userControls/GetExcel.aspx?T=CRG&P=01-01-2007&variation=PT 
  

，可以在浏览器工具中查看

302重定向，并且实际上是从以下URL下载文件

  http://www.centrodeinformacao.ren.pt/_layouts/CI .GetExcel / SafeGetExcel.aspx？T = CRG& P = 02-01-2007& variation = PT 
  

下一张图片（请求URL）

如果我转到手动两个链接，.xls文件下载就很好了o我们最好还是使用重定向后的那个。

---

我决定继续使用

2. 打开命令提示符，cd C：/ Program Files / vcpkg，运行 bootstrap-vcpkg.bat

和运行后 vcpkg集成安装

---

2。安装libcurl

1. 运行 vcpkg安装curl

---

3。创建一个新项目

1. 只需创建Visual C ++> Windows桌面> Windows控制台应用程序

可以使用 #include< curl / curl.h> 立即

---

4。当前结果

然后，从以下答案中得到启发

• 解决方案

  一次到该特定URL，将下载.xls文件。我不介意使用XLS而不是CSV，因此将其更改为我可以按预期方式获取文件。

    downloadFile（ ； http：//www.centrodeinformacao.ren.pt/_layouts/CI.GetExcel/SafeGetExcel.aspx？T = CRG& P = 01-01-2007&variation = PT， C：\\Users＼  molecoder桌面 test.xls）； 
    

  
  

  这是最终代码

    #include pch.h 
  ＃定义_CRT_SECURE_NO_WARNINGS 
   #include< iostream> 
   #include< iostream> 
   #include< stdio.h> 
   #include< curl / curl.h> 
   #include< string.h> 
   
   size_t write_data（void * ptr，size_t size，size_t nmemb，FILE * stream）{
   size_t写= fwrite（ptr，size，nmemb，流）; 
  书面回报； 
  } 
   
  无效downloadFile（const char * url，const char * fname）{
   CURL * curl; 
  文件* fp; 
   CURLcode res; 
   curl = curl_easy_init（）; 
   if（curl）{
   fp = fopen（fname， wb）; 
   curl_easy_setopt（curl，CURLOPT_URL，url）; 
   curl_easy_setopt（curl，CURLOPT_WRITEFUNCTION，write_data）; 
   curl_easy_setopt（curl，CURLOPT_WRITEDATA，fp）; 
   res = curl_easy_perform（curl）; 
   curl_easy_cleanup（curl）; 
   fclose（fp）; 
  } 
  } 
   
   int main（void）{
   
   downloadFile（ http://www.centrodeinformacao.ren.pt/_layouts/ CI.GetExcel / SafeGetExcel.aspx？T = CRG& P = 01-01-2007& variation = PT， C：\\Users\\molecoder\\Desktop\\test。 xls）； 
   
  } 
    

  
  

  My goal is to get a CSV or XLS from a specific URL using Cpp.

  When opening the following link

  http://www.centrodeinformacao.ren.pt/userControls/GetExcel.aspx?T=CRG&P=01-01-2007&variation=PT
  

  , can see in Browser tools

  a 302 redirect and the file being actually downloaded from the following URL

  http://www.centrodeinformacao.ren.pt/_layouts/CI.GetExcel/SafeGetExcel.aspx?T=CRG&P=02-01-2007&variation=PT
  

  as shown in the next image (Request URL)

  If I go to any of the two links manually, the a .xls file downloads just fine so we might as well use the one after redirection.

  ---

  I've decided to move on an use libcurl with Visual Studio 2017 on my W10 machine. The recommended way to include libcurl in a Visual Studio 2017 project is to use vcpkg and that's what I used.

  ---

  1. Install vcpkg

  1. Open Git Bash, cd C:/Program Files/ and cloned this repo.
  2. Open Command Prompt, cd C:/Program Files/vcpkg, run bootstrap-vcpkg.bat

  and after run vcpkg integrate install

  ---

  2. Install libcurl

  1. Run vcpkg install curl

  ---

  3. Create a new project

  1. Simply create Visual C++ > Windows Desktop > Windows Console Application

  to be able to use #include <curl/curl.h> right away

  ---

  4. Current Result

  Then, inspired in the following answers

  • https://stackoverflow.com/a/6951203/9415908

  • https://stackoverflow.com/a/1636415/9415908

  And using the following code

  #include "pch.h"
  #define _CRT_SECURE_NO_WARNINGS
  #include <iostream>
  #include <iostream>
  #include <stdio.h>
  #include <curl/curl.h>
  #include <string.h>
  
  size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
      size_t written = fwrite(ptr, size, nmemb, stream);
      return written;
  }
  
  void downloadFile(const char* url, const char* fname) {
      CURL *curl;
      FILE *fp;
      CURLcode res;
      curl = curl_easy_init();
      if (curl) {
          fp = fopen(fname, "wb");
          curl_easy_setopt(curl, CURLOPT_URL, url);
          curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
          curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
          res = curl_easy_perform(curl);
          curl_easy_cleanup(curl);
          fclose(fp);
      }
  }
  
  int main(void) {
  
      downloadFile("http://www.centrodeinformacao.ren.pt/_layouts/CI.GetExcel/SafeGetExcel.aspx?T=CRG&P=01-01-2007&variation=PT", "C:\\Users\\molecoder\\Desktop\\test.csv");
  
  }
  

  I can see a test.csv in the desired folder but it's an empty file.

  解决方案

  Once going to that specific URL, a .xls file downloads. I don't mind getting a XLS instead of a CSV and so changing it to I was able to get the file as expected.

  downloadFile("http://www.centrodeinformacao.ren.pt/_layouts/CI.GetExcel/SafeGetExcel.aspx?T=CRG&P=01-01-2007&variation=PT", "C:\\Users\\molecoder\\Desktop\\test.xls");
  

  This is the final code

  #include "pch.h"
  #define _CRT_SECURE_NO_WARNINGS
  #include <iostream>
  #include <iostream>
  #include <stdio.h>
  #include <curl/curl.h>
  #include <string.h>
  
  size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
      size_t written = fwrite(ptr, size, nmemb, stream);
      return written;
  }
  
  void downloadFile(const char* url, const char* fname) {
      CURL *curl;
      FILE *fp;
      CURLcode res;
      curl = curl_easy_init();
      if (curl) {
          fp = fopen(fname, "wb");
          curl_easy_setopt(curl, CURLOPT_URL, url);
          curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
          curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
          res = curl_easy_perform(curl);
          curl_easy_cleanup(curl);
          fclose(fp);
      }
  }
  
  int main(void) {
  
      downloadFile("http://www.centrodeinformacao.ren.pt/_layouts/CI.GetExcel/SafeGetExcel.aspx?T=CRG&P=01-01-2007&variation=PT", "C:\\Users\\molecoder\\Desktop\\test.xls");
  
  }
  

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