This command line utility prints out how WinINet, which is used by Internet Explorer, processes URLs, via InternetCombineUrl which combines a base reference with a relative reference, and via InternetCrackUrl, which splits URLs into various components. Originally http://lists.w3.org/Archives/Public/www-archive/2011Aug/0000.html

urlcrack.c

#undef UNICODE
#include <Windows.h>
#include <WinInet.h>
#include <stdio.h>

#pragma comment(lib, "wininet.lib")

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

  if (argc != 2 && argc != 3) {
    printf("Usage: `%s <URL>`, or `%s <Base> <Relative>`\n",
      argv[0], argv[0]);
    return 1;
  }

  DWORD length = 1024;
  char temp[1024];
  char* absolute = argv[1];

  if (argc == 3) {
    if (!InternetCombineUrl(argv[1], argv[2], temp, &length, 0))
      return GetLastError();
    absolute = temp;
  }

  URL_COMPONENTS parts;

  memset(&parts, 0, sizeof(parts));

  parts.dwStructSize      = sizeof(parts);
  parts.dwSchemeLength    = 1;
  parts.dwHostNameLength  = 1;
  parts.dwUserNameLength  = 1;
  parts.dwPasswordLength  = 1;
  parts.dwUrlPathLength   = 1;
  parts.dwExtraInfoLength = 1;

  if (!InternetCrackUrl(absolute, strlen(absolute), 0, &parts))
    return GetLastError();

  printf(""
    "Absolute:  %s\n"
    "Scheme:    %.*s\n"
    "HostName:  %.*s\n"
    "UserName:  %.*s\n"
    "Password:  %.*s\n"
    "UrlPath:   %.*s\n"
    "ExtraInfo: %.*s\n",
    absolute,
    parts.dwSchemeLength,
    parts.lpszScheme,
    parts.dwHostNameLength,
    parts.lpszHostName,
    parts.dwUserNameLength,
    parts.lpszUserName,
    parts.dwPasswordLength,
    parts.lpszPassword,
    parts.dwUrlPathLength,
    parts.lpszUrlPath,
    parts.dwExtraInfoLength,
    parts.lpszExtraInfo
  );

  return 0;
}