Replace traditional `#ifndef`/`#define`/`#endif` include guards with
`#pragma` once.
`#pragma once` is a widely supported preprocessor directive that
prevents header files from being included multiple times. It is
supported by all toolchains used to build edk2: GCC, Clang/LLVM, and
MSVC.
Compared to macro-based include guards, `#pragma once`:
- Eliminates the risk of macro name collisions or copy/paste errors
where two headers inadvertently use the same guard macro.
- Eliminate inconsistency in the way include guard macros are named
(e.g., some files use `__FILE_H__`, others use `FILE_H_`, etc.).
- Reduces boilerplate (three lines replaced by one).
- Avoids polluting the macro namespace with guard symbols.
- Can improve build times as the preprocessor can skip re-opening the
file entirely, rather than re-reading it to find the matching
`#endif` ("multiple-include optimization").
- Note that some compilers may already optimize traditional include
guards, by recognzining the idiomatic pattern.
This change is made acknowledging that overall portability of the
code will technically be reduced, as `#pragma once` is not part of the
C/C++ standards.
However, this is considered acceptable given:
1. edk2 already defines a subset of supported compilers in
BaseTools/Conf/tools_def.template, all of which have supported
`#pragma once` for over two decades.
2. There have been concerns raised to the project about inconsistent
include guard naming and potential macro collisions.
Approximate compiler support dates:
- MSVC: Supported since Visual C++ 4.2 (1996)
- GCC: Supported since 3.4 (2004)
(http://gnu.ist.utl.pt/software/gcc/gcc-3.4/changes.html)
- Clang (LLVM based): Since initial release in 2007
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
The UefiShell*CommandsLib instances have constructor functions that do
something like:
gHiiHandle = HiiAddPackages (...);
...
ShellCommandRegisterCommandName (..., gHiiHandle, ...);
and destructor functions that implement the following pattern:
HiiRemovePackages (gHiiHandle);
The -- semantic, not functional -- problem is that "gHiiHandle" is
declared with type EFI_HANDLE, and not EFI_HII_HANDLE, in all of these
library instances, even though HiiAddPackages() correctly returns
EFI_HII_HANDLE, and HiiRemovePackages() takes EFI_HII_HANDLE.
Once we fix the type of "gHiiHandle", it causes sort of a butterfly
effect, because it is passed around widely. Track down and update all of
those locations.
The DynamicCommand lib instances use a similar pattern, so they are
affected too.
NOTE: in practice, this patch is a no-op, as both EFI_HII_HANDLE and
EFI_HANDLE are typedefs to (VOID*). However, we shouldn't use EFI_HANDLE
where semantically EFI_HII_HANDLE is passed around.
Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Zhichao Gao <zhichao.gao@intel.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Zhichao Gao <zhichao.gao@intel.com>
echo - add input verificaiton.
help - prints out commands in sorted order.
touch - add comments.
type - add error when file not found. add comments.
main lib files:
add comments, clarify error messages.
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11427 6f19259b-4bc3-4df7-8a09-765794883524
