Currently in the entire C API of WPILib we have ~8 different ways of handling strings. The C API actually isn't built for pure C callers (We don't actually have any of those). Instead, they're built for interop between languages like LabVIEW and C# which can talk to C API's directly.
For output parameters, the choice was fairly obvious. An output struct containing a const string pointer and a length makes the most sense. Its easy to use these from most other languages, and doesn't require special null termination handling. Freeing these is also easy, as if you ever receive one of these string structures, theres just a single function call to free it.
Input parameters are a bit more complex. To be used from pure C, and from LabVIEW, a null terminated string is the best in most cases. However, null terminated strings in general have a lot of downsides. Additionally, from LabVIEW there are other considerations around encoding that having a wrapper struct helps make a bit easier. From a language like C#, a wrapper struct is by far the easiest, as custom marshalling can make it trivial to marshal both UTF8 and UTF16 strings down.
The final consideration is its nice to have an identical concept for both input and output. It makes the rules fairly easy to understand.
WPILib will not have any APIs that manipulate a string allocated externally. This means WPI_String can be const, as across the boundary it is always const.
If a WPILib API takes a const WPI_String*, WPILib will not manipulate or attempt to free that string, and that string is treated as an input. It is up to the caller to handle that memory, WPILib will never hold onto that memory longer than the call.
If a WPILib API takes a WPI_String*, that string is an output. WPILib will allocate that API with WPI_AllocateString(), fill in the string, and return to the caller. When the caller is done with the string, they must free it with WPI_FreeString().
If an output struct contains a WPI_String member, that member is considered read only, and should not be explicitly freed. The caller should call the free function for that struct.
If an array of WPI_Strings are returned, each individual string is considered read only, and should not be explicitly freed. The free function for that array should be called by the caller.
If an input struct containing a WPI_String, or an input array of WPI_Strings is passed to WPILib, the individual strings will not be manipulated or freed by WPILib, and the caller owns and should free that memory.
Callbacks also follow these rules. The most common is a callback either getting passed a const WPI_String* or a struct containing a WPI_String. In both of these cases, the callback target should consider these strings read only, and not attempt to free them or manipulate them.
We now use a wrapper (wpi::print) to catch exceptions since we can't patch
std::print() to not throw when we ultimately migrate to it.
fmtlib and std format/print throw the same exceptions and always have. We previously patched fmt::print() to not throw a write failure exception, but we can't do that for std::print(); wpi::print() is the migration plan.
Eventually we want to get to a point where we can remove OpenCV from the internals of cscore. The start to doing that is converting the existing CvSource and CvSink methods to RawFrame.
For CvSource, this is 100% a free operation. We can do everything the existing code could have done (with one small exception we can fairly easily fix).
For CvSink, by defaut this change would incur one extra copy, but no extra allocations. A set of direct methods were added to CvSink to add a method to avoid this extra copy.
The main restriction is there must be an event loop running on the main thread.
No special action is required for GUI applications, but for non-GUI applications, a
RunOsxRunLoop() function is provided that needs to be called from the main thread.
This is enabled by the C++20 __VA_OPT__ feature.
Uses of "{}" format string were updated.
Some warning suppressions were required for older clang versions.
Also improve codegen of wpi::Logger::Log(), frc::ReportError(), and frc::MakeError();
these generate better and less redundant code if they use fmt::string_view for the
format string instead of templating on it.
* Use explicit this capture required by C++20
* Use C++20 span
* Replace wpi::numbers with std::numbers
* Fix C++20 clang-tidy warning false positive in fmt
* Remove ciso646 include since C++20 removed that header
* Fix global-buffer-overflow asan warnings in ntcore tests
* Add DIOSetProxy constructor to HAL
* Upgrade MSVC compiler to 2022
* Bump native-utils to 2023.2.7 (changes to std=c++20)
Co-authored-by: Peter Johnson <johnson.peter@gmail.com>
fmt removed fmt::make_args_checked since it's no longer needed for
constexpr format string checks.
fmt deprecated implicit conversions from enums to integers in format
arguments, so I added explicit static casts.
Unlike std::string and std::string_view, this substr() allows a start
greater than the length of the string, in which case an empty string
is returned. This matches llvm::StringRef behavior.
These relied on the OnStart and OnExit callbacks which were not present
in the wpiutil common CallbackManager code. Add support for these and
fix up other use cases.
Also fixes notifications to correctly filter on event kind.
This fixes a breakage caused by #3133.
- Twine, StringRef, Format, and NativeFormatting have been removed
- Logging now uses fmtlib style formatting
- Nearly all uses of wpi::outs/errs have been replaced with fmt::print() or
std::puts()/std::fputs() (for unformatted strings).
- A wpi/fmt/raw_ostream.h header has been added to enable
fmt::print() with wpi::raw_ostream
Use ghc::filesystem as fill on older GCC (e.g. RoboRIO).
This can be removed once all GCC platforms have upgraded to 8.1 or later.
File open functionality has been retained from LLVM but moved to "fs" namespace
and tweaked for improved consistency with std::filesystem (e.g. error_code is
passed by reference instead of returned).
Also update WPILibC's Filesystem functions to return std::string.
* Add .clang-tidy configuration.
* A separate .clang-tidy is used for hal includes to suppress modernize-use-using
(as these are C headers).
* Add NOLINT where necessary for a clean run.
* Add clang-tidy job to lint-format workflow. This workflow is now only run on PRs.
To reduce runtime, clang-tidy is only run on files changed in the PR.
Two wpilibc changes; both are unlikely to break user code:
* BuiltInAccelerometer: Make SetRange() final
* Counter: Make SetMaxPeriod() final
After these cleanups, the only file that does not run cleanly is
cscore_raw_cv.h due to it not being standalone.
