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ThorsLogging Internal Documentation

Implementation details, macro machinery, and build-mode internals for the ThorsLogging library.

Source: third/ThorsLogging/src/ThorsLogging/

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Architecture

The entire public surface is in a single header: ThorsLogging.h. There are no additional .cpp files; the implementation is entirely macro- and inline-based.

ThorsLogging.h          <-- Public API (macros + ThorsLogTemp class)
ThorsLoggingConfig.h    <-- Generated build configuration

Dependencies

• loguru – bundled as a git submodule under third/loguru/
• ThorsIOUtil – provides ThorsAnvil::Utility::buildErrorMessage() for formatting all log messages

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Build Modes

Controlled by the preprocessor symbol THORS_LOGGING_HEADER_ONLY:

Mode	THORS_LOGGING_HEADER_ONLY	Backend	Notes
Linked	0 or undefined	loguru	Full loguru functionality; requires linking against loguru.
Header-only	1	std::cerr	No link dependency. Minimal loguru::NamedVerbosity enum provided.

In header-only mode, THOR_LOGGING_DEFAULT_LOG_LEVEL (default: 3) determines which messages are emitted. Messages with verbosity numerically greater than this threshold are suppressed at compile time.

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Verbosity Model

Inherits loguru’s verbosity model. Lower numeric values are more severe:

Named Level	Numeric	Macro Suffix
FATAL	-3	Fatal
ERROR	-2	Error
WARNING	-1	Warning
INFO	0	Info
(debug)	3	Debug
(track)	5	Track
(trace)	7	Trace
(all)	9	All

Special values:

• Verbosity_OFF (-9) – suppress all output
• Verbosity_INVALID (-10) – sentinel; never log at this level

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Internal Macro Machinery

Core Implementation Macro

ThorsLogActionWithPotetialThrow(hasExcept, Exception, Level, Scope, Function, ...)

When hasExcept is true, it logs and throws. When false, it only logs. The throw path uses if constexpr so it is compiled away when not needed.

Wrapper Macros

• ThorsLogAction(...) – calls core macro with hasExcept=false and Exception=std::runtime_error (unused).
• ThorsLogAndThrowAction(...) – calls core macro with hasExcept=true.

Message Formatting

All messages are formatted via ThorsAnvil::Utility::buildErrorMessage(...) which concatenates all variadic arguments using operator<< to a std::ostringstream.

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Header-Only Mode Internals

When THORS_LOGGING_HEADER_ONLY == 1:

ConvertToVoid

A helper class whose operator&(std::ostream&) discards the stream expression. Used by VLOG_IF_S to conditionally suppress output at compile time.

VLOG_IF_S(verbosity, cond)

Expands to either (void)0 (suppressed) or std::cerr (active), based on verbosity and condition.

VLOG_S(verbosity)

Shorthand for VLOG_IF_S(verbosity, true).

ThorsLogOutput(Level, message)

Writes to std::cerr if the level is within threshold.

ThorsLogTemp (Header-Only)

In header-only mode, ThorsLogTemp is a no-op (constructor/destructor do nothing).

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Linked Mode Internals

In linked mode, the macros delegate to loguru’s VLOG_S / LOG_F macros, which provide:

• Colored console output
• File logging
• Syslog support
• Stack traces on fatal errors
• Thread-safe output

ThorsLogFatal causes the application to abort via loguru’s FATAL handling.

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Configuration Reference

Preprocessor Symbols

Symbol	Default	Description
THORS_LOGGING_HEADER_ONLY	0	Set to 1 for header-only mode
THOR_LOGGING_DEFAULT_LOG_LEVEL	3	Header-only compile-time verbosity ceiling
LOGURU_WITH_STREAMS	1	Enables loguru’s stream-based API. Always set.

Build System

• configure.ac defines the project and checks for libdl.
• AX_THOR_FEATURE_HEADER_ONLY_VARIANT(THORS_LOGGING) provides --enable-header-only.
• ThorsLoggingConfig.h is generated from config.h.in.
• The Makefile adds -DLOGURU_WITH_STREAMS=1 to CXXFLAGS.

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