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Diffstat (limited to 'absl/log/log_streamer.h')
| -rw-r--r-- | absl/log/log_streamer.h | 176 |
1 files changed, 176 insertions, 0 deletions
diff --git a/absl/log/log_streamer.h b/absl/log/log_streamer.h new file mode 100644 index 00000000..c3776cec --- /dev/null +++ b/absl/log/log_streamer.h @@ -0,0 +1,176 @@ +// Copyright 2022 The Abseil Authors. +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// https://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. +// +// ----------------------------------------------------------------------------- +// File: log/log_streamer.h +// ----------------------------------------------------------------------------- +// +// This header declares the class `LogStreamer` and convenience functions to +// construct LogStreamer objects with different associated log severity levels. + +#ifndef ABSL_LOG_LOG_STREAMER_H_ +#define ABSL_LOG_LOG_STREAMER_H_ + +#include <ios> +#include <memory> +#include <ostream> +#include <string> +#include <utility> + +#include "absl/base/config.h" +#include "absl/base/log_severity.h" +#include "absl/log/log.h" +#include "absl/memory/memory.h" +#include "absl/strings/internal/ostringstream.h" +#include "absl/strings/string_view.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN + +// LogStreamer +// +// Although you can stream into `LOG(INFO)`, you can't pass it into a function +// that takes a `std::ostream` parameter. `LogStreamer::stream()` provides a +// `std::ostream` that buffers everything that's streamed in. The buffer's +// contents are logged as if by `LOG` when the `LogStreamer` is destroyed. +// If nothing is streamed in, an empty message is logged. If the specified +// severity is `absl::LogSeverity::kFatal`, the program will be terminated when +// the `LogStreamer` is destroyed regardless of whether any data were streamed +// in. +// +// Factory functions corresponding to the `absl::LogSeverity` enumerators +// are provided for convenience; if the desired severity is variable, invoke the +// constructor directly. +// +// LogStreamer is movable, but not copyable. +// +// Examples: +// +// ShaveYakAndWriteToStream( +// yak, absl::LogInfoStreamer(__FILE__, __LINE__).stream()); +// +// { +// // This logs a single line containing data streamed by all three function +// // calls. +// absl::LogStreamer streamer(absl::LogSeverity::kInfo, __FILE__, __LINE__); +// ShaveYakAndWriteToStream(yak1, streamer.stream()); +// streamer.stream() << " "; +// ShaveYakAndWriteToStream(yak2, streamer.stream()); +// streamer.stream() << " "; +// ShaveYakAndWriteToStreamPointer(yak3, &streamer.stream()); +// } +class LogStreamer final { + public: + // LogStreamer::LogStreamer() + // + // Creates a LogStreamer with a given `severity` that will log a message + // attributed to the given `file` and `line`. + explicit LogStreamer(absl::LogSeverity severity, absl::string_view file, + int line) + : severity_(severity), + line_(line), + file_(file), + stream_( + absl::make_unique<absl::strings_internal::OStringStream>(&buf_)) { + // To match `LOG`'s defaults: + stream_->setf(std::ios_base::showbase | std::ios_base::boolalpha); + } + + // A moved-from `absl::LogStreamer` does not `LOG` when destroyed, + // and a program that streams into one has undefined behavior. + LogStreamer(LogStreamer&& that) noexcept + : severity_(that.severity_), + line_(that.line_), + file_(std::move(that.file_)), + buf_(std::move(that.buf_)), + stream_(that.stream_ + ? absl::make_unique<absl::strings_internal::OStringStream>( + &buf_) + : nullptr) { + that.stream_.reset(); + } + LogStreamer& operator=(LogStreamer&& that) { + LOG_IF(LEVEL(severity_), stream_).AtLocation(file_, line_) << buf_; + severity_ = that.severity_; + file_ = std::move(that.file_); + line_ = that.line_; + buf_ = std::move(that.buf_); + stream_ = + that.stream_ + ? absl::make_unique<absl::strings_internal::OStringStream>(&buf_) + : nullptr; + that.stream_.reset(); + return *this; + } + + // LogStreamer::~LogStreamer() + // + // Logs this LogStreamer's buffered content as if by LOG. + ~LogStreamer() { + LOG_IF(LEVEL(severity_), stream_).AtLocation(file_, line_) << buf_; + } + + // LogStreamer::stream() + // + // Returns the `std::ostream` to use to write into this LogStreamer' internal + // buffer. + std::ostream& stream() { return *stream_; } + + private: + absl::LogSeverity severity_; + int line_; + std::string file_; + std::string buf_; + // TODO(durandal): de-pointerize this once we are off of our old mostly-C++11 + // libstdc++ (which lacks move constructors for std streams). + // `stream_` is null in a moved-from `LogStreamer`; this is in fact how we + // recognize one to avoid logging when it is destroyed or reassigned. + std::unique_ptr<absl::strings_internal::OStringStream> stream_; +}; + +// LogInfoStreamer() +// +// Returns a LogStreamer that writes at level LogSeverity::kInfo. +inline LogStreamer LogInfoStreamer(absl::string_view file, int line) { + return absl::LogStreamer(absl::LogSeverity::kInfo, file, line); +} + +// LogWarningStreamer() +// +// Returns a LogStreamer that writes at level LogSeverity::kWarning. +inline LogStreamer LogWarningStreamer(absl::string_view file, int line) { + return absl::LogStreamer(absl::LogSeverity::kWarning, file, line); +} + +// LogErrorStreamer() +// +// Returns a LogStreamer that writes at level LogSeverity::kError. +inline LogStreamer LogErrorStreamer(absl::string_view file, int line) { + return absl::LogStreamer(absl::LogSeverity::kError, file, line); +} + +// LogFatalStreamer() +// +// Returns a LogStreamer that writes at level LogSeverity::kFatal. +// +// The program will be terminated when this `LogStreamer` is destroyed, +// regardless of whether any data were streamed in. +inline LogStreamer LogFatalStreamer(absl::string_view file, int line) { + return absl::LogStreamer(absl::LogSeverity::kFatal, file, line); +} + +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_LOG_LOG_STREAMER_H_ |