---
name: "nng_log_set_logger"
section: "3"
platform: "linux"
package: "libnng-dev"
version: "1.10.1-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/nng_log_set_logger"
---

# nng\_log\_set\_logger(3)

set logging handler

## 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_facility/3.md), [nng\_log\_set\_level(3)](/nng_log_set_level/3.md), [nng\_log(3)](/nng_log/3.md)