下載文件要用到操作系統的API函數，下面是一個WINDOWS系統中的實現：

//---------------------------------------------------------------------------
#include "stdafx.h"
#include <stdio.h>
#include <windows.h>
#include <wininet.h>
#define MAXBLOCKSIZE 1024
#pragma comment( lib, "wininet.lib" ) ;

void download(const char *Url,const char *save_as)/*將Url指向的地址的文件下載到save_as指向的本地文件*/
{
 byte Temp[MAXBLOCKSIZE];
 ULONG Number = 1;

 FILE *stream;
 HINTERNET hSession = InternetOpen(_T("RookIE/1.0"), INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0);
 if (hSession != NULL)
 {
  HINTERNET handle2 = InternetOpenUrl(hSession,_T(Url), NULL, 0, INTERNET_FLAG_DONT_CACHE, 0);
  if (handle2 != NULL)
  {

   if( (stream = fopen( save_as, "wb" )) != NULL )
   {
    while (Number > 0)
    {
     InternetReadFile(handle2, Temp, MAXBLOCKSIZE - 1, &Number);

     fwrite(Temp, sizeof (char), Number , stream);
    }
    fclose( stream );
   }

   InternetCloseHandle(handle2);
   handle2 = NULL;
  }
  InternetCloseHandle(hSession);
  hSession = NULL;
 }
}

int main(int argc, char* argv[]){

 download("*調用示例，下載百度的首頁到c:\index.html文件*/
 return 0;
}