I am copying my question from stackoverflow:
I wrote a simple application on Qt4 that modifier network adapter parameters, for that I have a slot called setInterfaceParams, implemented as so:
Qt Code: 
  1. DWORD WinNetInterface::setInterfaceParams(QString index, QString ip, QString netmask, QString gateway)
  2. {
  3.     DWORD res = NULL;
  4.     HINSTANCE lib = (HINSTANCE) LoadLibrary((WCHAR *)"iphlpapi.dll");
  5.     _SetAdapterIpAddress SetAdapterIpAddress = (_SetAdapterIpAddress) GetProcAddress(lib, "SetAdapterIpAddress");
  6.  
  7.     PWSTR pszGUID = NULL;
  8.     //char  *szGUID = (char *)index.toStdString().c_str();
  9.     QByteArray a = index.toLocal8Bit();
  10.     char  *szGUID = a.data();
  11.     WideCharToMultiByte(CP_ACP, 0, pszGUID, -1, szGUID, sizeof(szGUID), NULL, NULL);
  12.  
  13.  
  14. // Method 01
  15.     res = SetAdapterIpAddress(szGUID,
  16.                         0,
  17.                         inet_addr(ip.toStdString().c_str()),
  18.                         inet_addr(netmask.toStdString().c_str()),
  19.                         inet_addr(gateway.toStdString().c_str()));
  20. // End of method 01
  21.  
  22. // Method 02
  23.     /*res = SetAdapterIpAddress("{422C5689-A17B-402D-A6A2-22CE13E857B5}",
  24.                                 0,
  25.                                 inet_addr("192.168.1.10"),
  26.                                 inet_addr("255.255.255.0"),
  27.                                 inet_addr("192.168.1.1"));*/
  28. // End of method 02
  29.     return res;
  30. }
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When I click on button that connected to slot setInterfaceParams, I get segmentation fault. If I comment method01, nothing happen, the some thing happen when I use method02. I tried this function on a simple c++ application and it is work fine, test on Windows XP SP3.
Qt Code: 
  1. #include <windows.h>
  2. #include <winsock2.h>
  3. #include <iphlpapi.h>
  4. #include <stdio.h>
  5. #include <iostream>
  6.  
  7.  
  8. typedef DWORD (WINAPI *_SetAdapterIpAddress )(char *szAdapterGUID, 
  9.                                               DWORD dwDHCP, 
  10.                                               DWORD dwIP, 
  11.                                               DWORD dwMask, 
  12.                                               DWORD dwGateway); 
  13.  
  14.  
  15. int main()
  16. {
  17.     HINSTANCE lib = (HINSTANCE) LoadLibrary("iphlpapi.dll"); 
  18.     _SetAdapterIpAddress SetAdapterIpAddress = (_SetAdapterIpAddress) GetProcAddress(lib, "SetAdapterIpAddress");
  19.  
  20.     PWSTR pszGUID = NULL;
  21.     char  szGUID[] = "{422C5689-A17B-402D-A6A2-22CE13E857B5}";
  22.     DWORD dwSize = 0;
  23.     WideCharToMultiByte(CP_ACP, 0, pszGUID, -1, szGUID, sizeof(szGUID), NULL, NULL);
  24.  
  25.     DWORD res = SetAdapterIpAddress(szGUID, 
  26.                         0, 
  27.                         inet_addr("192.168.1.10"),
  28.                         inet_addr("255.255.255.0"),
  29.                         inet_addr("192.168.1.1"));
  30.  
  31.     std::cout << res;                   
  32.  
  33.     return 0;
  34. }
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