---
name: "nng_log"
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"
---

# nng\_log(3)

log messages

## NAME

nng\_log - log messages

## SYNOPSIS

```
#include <nng/nng.h>
void nng_log_err(const char *msgid, const char *msg, ...);
void nng_log_warn(const char *msgid, const char *msg, ...);
void nng_log_notice(const char *msgid, const char *msg, ...);
void nng_log_info(const char *msgid, const char *msg, ...);
void nng_log_debug(const char *msgid, const char *msg, ...);
void nng_log_auth(nng_log_level level, const char *msgid, const char *msg, ...);
```

## DESCRIPTION

These functions are used to post a message to system or application logs.

The first five forms all post a message at the severity indicated by the function name. The *msgid* should be a short message identifier that should indicate the message in question. A `NULL` value for *msgid* canbe used as well.

Message identifiers can be used to assist in filtering logs. These should uniquely identify the nature of the problem, whe possible, to assist in trouble-shooting. They should also be short. Eight characters or less is ideal, and more than sixteen is strongly discouraged.

The message is formatting as if by `sprintf`, using `msg` as the format, and remaining arguments as arguments to the format.

The final function, `nng_log_auth`, is used for posting authentication related messages which might be treated specially, such as be storing them in a separate secured log file. It takes the severity as a level in *level*. The severity can be one of the following values:

• `NNG_LOG_ERR`

• `NNG_LOG_WARN`

• `NNG_LOG_NOTICE`

• `NNG_LOG_INFO`

• `NNG_LOG_DEBUG`

The message itself is handled according to the logging facility set up with `nng_log_set_logger`. Message delivery is best effort, and messages may be suppressed based on the priority set with `nng_log_set_level`.

Note that in order to get log messages, a suitable logger must be set using `nng_log_set_logger`. The default logger, `nng_null_logger` simply discards logged content.

## 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\_set\_logger(3)](/nng_log_set_logger/3.md)