Module log

A lightweight logging facade for Rust.

• Crate ::log.
• docs.rs
• crates.io
• GitHub

---

log provides a single logging API that abstracts over the actual logging implementation. Libraries can use the logging API provided by this crate, and the executable can choose the logging implementation that is most suitable for its use case.

The log crate provides macros for logging at various levels: error!, warn!, info!, debug!, and trace!, where error! represents the highest priority and trace! the lowest.

The logging facade itself doesn’t perform any logging; it needs to be paired with a logging implementation like env_logger, simplelog, fern, or tracing-subscriber. The implementation is responsible for filtering log messages, formatting them, and outputting them to the appropriate destination.

Examples

use log::{debug, error, info, trace, warn};

fn main() {
    env_logger::init();

    process_data(42);
}

fn process_data(value: i32) {
    trace!("Starting data processing");
    debug!("Processing value: {}", value);

    if value < 0 {
        error!("Invalid value: {}", value);
        return;
    }

    if value == 0 {
        warn!("Processing zero value");
    }

    info!("Successfully processed value: {}", value);
}

Macros

debug

Logs a message at the debug level.

error

Logs a message at the error level.

info

Logs a message at the info level.

log

The standard logging macro.

log_enabled

Determines if a message logged at the specified level in that module will be logged.

trace

Logs a message at the trace level.

warn

Logs a message at the warn level.

Structs

Metadata

Metadata about a log message.

MetadataBuilder

Builder for Metadata.

ParseLevelError

The type returned by from_str when the string doesn’t match any of the log levels.

Record

The “payload” of a log message.

RecordBuilder

Builder for Record.

SetLoggerError

The type returned by set_logger if set_logger has already been called.

Enums

Level

An enum representing the available verbosity levels of the logger.

LevelFilter

An enum representing the available verbosity level filters of the logger.

Constants

STATIC_MAX_LEVEL

The statically resolved maximum log level.

Traits

Log

A trait encapsulating the operations required of a logger.

Functions

logger

Returns a reference to the logger.

max_level

Returns the current maximum log level.

set_boxed_logger

Sets the global logger to a Box<Log>.

set_logger

Sets the global logger to a &'static Log.

set_logger_racy^⚠

A thread-unsafe version of set_logger.

set_max_level

Sets the global maximum log level.

set_max_level_racy^⚠

A thread-unsafe version of set_max_level.