# nng_log_set_logger(3) Manual Page

## NAME

nng_log_set_logger - set logging handler

## SYNOPSIS

    #include <nng/nng.h>

    typedef void (*nng_logger)(nng_log_level level, nng_log_facility facility,
        const char *msgid, const char *msg);

    void nng_null_logger(nng_log_level, nng_log_facility, const char *, const char *);
    void nng_stderr_logger(nng_log_level, nng_log_facility, const char *, const char *);
    void nng_system_logger(nng_log_level, nng_log_facility, const char *, const char *);

    void nng_log_set_logger(nng_logger logger);

## DESCRIPTION

The `nng_log_set_logger` is used to set the base logging function to logger. The logger may be a user defined function to process log messages. Only a single logger may be registered at a time. If needed, the logger should make copies of either msgid or msg, as those may not be valid once the logger function returns.

The `nng_null_logger` function is an implementation of `nng_logger` that simply discards the content. This is the default logger, so logging is disabled by default.

The `nng_stderr_logger` function is an implementation that logs messages to the standard error stream. It will attempt to colorize messages by the severity, if the standard error is a terminal device. This can be supressed by setting either the `NO_COLOR` or `NNG_LOG_NO_COLOR` environment variables.

The `nng_system_logger` attempts to use an appropriate system facility to log messages. For POSIX systems, this means using `syslog` to process the messages. For other the `nng_stderr_log` may be used as a fallback.

## SEE ALSO

nng_log_set_facility(3), nng_log_set_level(3), nng_log(3)