Is it OK to Edit GCC Header Files? - c++

Question

I was trying to compile some example code from MSDN with GCC on Windows 7 (please ignore the use of goto and the terrible formatting; it's not my code):
#include <stdio.h>
#include <windows.h>
typedef struct _TOKEN_ELEVATION {
DWORD TokenIsElevated;
} TOKEN_ELEVATION, *PTOKEN_ELEVATION;
BOOL IsProcessElevated()
{
BOOL fIsElevated = FALSE;
DWORD dwError = ERROR_SUCCESS;
HANDLE hToken = NULL;
if (!OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &hToken))
{
dwError = GetLastError();
goto Cleanup;
}
TOKEN_ELEVATION elevation;
DWORD dwSize;
if (!GetTokenInformation(hToken, TokenElevation, &elevation,
sizeof(elevation), &dwSize))
{
dwError = GetLastError();
goto Cleanup;
}
fIsElevated = elevation.TokenIsElevated;
Cleanup:
if (hToken)
{
CloseHandle(hToken);
hToken = NULL;
}
if (ERROR_SUCCESS != dwError)
{
throw dwError;
}
return fIsElevated;
}
int main()
{
try
{
if (IsProcessElevated())
wprintf (L"Process is elevated\n");
else
wprintf (L"Process is not elevated\n");
}
catch (DWORD dwError)
{
wprintf(L"IsProcessElevated failed w/err %lu\n", dwError);
}
}
I kept getting the error TokenElevation was not declared in this scope. While trying to figure it out I saw that the TokenElevation member of the TOKEN_INFORMATION_CLASS struct was between two #ifdef tags:
typedef enum _TOKEN_INFORMATION_CLASS {
TokenUser=1,
TokenGroups,
TokenPrivileges,
TokenOwner,
TokenPrimaryGroup,
TokenDefaultDacl,
TokenSource,
TokenType,
TokenImpersonationLevel,
TokenStatistics,
TokenRestrictedSids,
TokenSessionId,
TokenGroupsAndPrivileges,
TokenSessionReference,
TokenSandBoxInert,
TokenAuditPolicy,
TokenOrigin,
//#if (_WIN32_WINNT >= 0x0600)
TokenElevationType,
TokenLinkedToken,
TokenElevation,
TokenHasRestrictions,
TokenAccessInformation,
TokenVirtualizationAllowed,
TokenVirtualizationEnabled,
TokenIntegrityLevel,
TokenUIAccess,
TokenMandatoryPolicy,
TokenLogonSid,
//#endif
MaxTokenInfoClass
} TOKEN_INFORMATION_CLASS;
I commented these out and the code compiled without errors or warnings. My question is really two questions. Is their a better way to do this (define something in my code?) and, in the long run, will editing header files hurt me?

Answer 1

Editing the headers will hurt because your code is no longer being built against an external library you simply depend on. Instead you have effectively made that external code part of your project, and now you have to manage it like other source code in your project. You should keep it in your version control system, for example.
Yes, there is a better way: you can simply define _WIN32_WINNT as the Windows code expects it to be defined. Visual Studio projects define this macro by default, but you have to do that manually when building with gcc on Windows.
This page defines the values for each version of Windows.

Answer 2

Yes, you can edit and change GCC header files.
Be aware that when GCC upgrades, your changes may be lost. You would have to merge your changes into the newer header files.
For this reason, common rule of thumb is not to modify compiler header files.
Edit 1:
Also, if you share your code, you will need to have the clients make the same mods to the GCC header files that you did. Some clients may not want their compiler header files changed. Same rules apply when you have other people working on the same project.
Also, will your changes affect future projects? Future projects may use the GCC header files also.

Answer 3

You can modify them but it is usually a bad idea, because it will make you compilation difficult to repeat.
In this particular case, the right solution is just to define _WIN32_WINNT as 0x0600 or higher. This macro is used to specify the Windows version you are targeting, and you clearly are targeting at least version 6, or you would not be able to use this value. The Windows SDK header files use this macro to conditially include declarations available in every version of Windows, so you cannot use a function/field/enum value from Windows 8 in a program intended to run in Windows 7, for example.
So just add -D_WIN32_WINNT=0x0600 to your compilation command and leave the header files alone...