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+# nng_log_logger
+
+## NAME
+
+nng_log_logger --- logging handler
+
+## SYNOPSIS
+
+```c
+#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
+
+An {{i:`nng_logger`}}{{hi:logger}} is a function used as a handler to process logged messages.
+This is responsible for the final disposition of the logged messages.
+
+The {{i:`nng_log_set_logger`}} function 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 they will not be valid after the logger returns.
+
+The {{i:`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 {{i:`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 {{i:`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 systems the defauilt behavior may be the same as `nng_stderr_logger`.
+
+## SEE ALSO
+
+[nng_log](./nng_log.md),
+[nng_log_facility](./nng_log_facility.md),
+[nng_log_level](./nng_log_level.md)