Configuration

Configuration

All settings are process-wide and can be changed at any time from any thread.

Enabling output

Logging is disabled by default. Nothing is written until enable_logging(). disable_logging() turns it off again, and log_is_enabled() returns the current state.

Levels

Level::Debug < Level::Info < Level::Warn < Level::Error. Messages below the minimum level are dropped. The default minimum is Info.

coretrace::set_min_level(coretrace::Level::Warn); // Warn and Error only
coretrace::Level current = coretrace::min_level();

The CT_LOG_LEVEL environment variable sets the startup default: debug, info, warn or error, case-insensitive. Any other value means info. A call to set_min_level() always wins over it.

Modules

A message can carry a module tag: log(Level::Info, Module("alloc"), "...").

• Until a module is enabled, every message passes.
• Once a module has been enabled with enable_module(), tagged messages pass only if their module is enabled. Messages without a tag always pass.
• disable_module() removes one name. It never lets more messages through: after the last name is removed, tagged messages stay filtered.
• enable_all_modules() clears the filter, and every message passes again.
• module_is_enabled(name) tells whether a tagged message with that name would pass.
• Module("") counts as untagged: it bypasses the filter and prints no tag.

Names are case-sensitive. The filter holds up to 32 names of at most 31 characters. enable_module() returns false, and changes nothing, for an empty name, a longer name, or a full table.

CT_DEBUG

CT_DEBUG=alloc,trace enables modules at startup. Spaces around names are ignored (CT_DEBUG="alloc, trace" works). Empty items are skipped, and so are names that do not fit the limits.

CT_LOG_LEVEL and CT_DEBUG are read once, at the first logger call that needs them (log(), a getter such as min_level(), or a filter setter) or, on POSIX, at the first fork(), whichever comes first. A module function called before that point makes the library ignore CT_DEBUG. Called afterwards, it changes the set loaded from CT_DEBUG.

Prefix

set_prefix("==myapp==") replaces the default ==ct== tag. The string is copied, and truncated to 63 characters.

Timestamps

set_timestamps(true) starts each line with an ISO 8601 UTC timestamp with milliseconds: [2026-09-30T08:15:02.417] .

Source location

set_source_location(true) adds file.cpp:42 after the level. The file name and line come from std::source_location at the call site. Level converts implicitly to LogEntry, which captures it.

Colors

The library colors its output when stderr is a terminal: isatty() on POSIX, or a console that accepts virtual terminal sequences on Windows. It decides once per process, on first use. A child of fork() keeps the decision the parent had already made. Setting NO_COLOR to any non-empty value disables colors. An empty NO_COLOR keeps them, as no-color.org specifies.

Level	Color
DEBUG	cyan
INFO	green
WARN	yellow
ERROR	red

color(Color::Bold) returns an escape sequence you can put in your own messages, or an empty string when colors are off. The decision is based on stderr even when a custom sink is installed. Set NO_COLOR=1 if a sink must not receive escape sequences.

Environment variables

Variable	Effect
CT_LOG_LEVEL	Startup minimum level: debug, info, warn, error (case-insensitive)
CT_DEBUG	Startup list of enabled modules, comma-separated
NO_COLOR	Disables colors when set to a non-empty value