---
name: "mongoc_unstructured_log"
section: "3"
platform: "linux"
package: "libmongoc-doc"
version: "1.30.4-1+deb13u3"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/mongoc_unstructured_log"
---

# mongoc\_unstructured\_log(3)

This is the original logging facility that supports freeform string messages originating from the driver itself or from application code. This has been retroactively termed "unstructured logging". See *Structured Logging* for the newer standardized logging facility.

```
typedef enum {
   MONGOC_LOG_LEVEL_ERROR,
   MONGOC_LOG_LEVEL_CRITICAL,
   MONGOC_LOG_LEVEL_WARNING,
   MONGOC_LOG_LEVEL_MESSAGE,
   MONGOC_LOG_LEVEL_INFO,
   MONGOC_LOG_LEVEL_DEBUG,
   MONGOC_LOG_LEVEL_TRACE,
} mongoc_log_level_t;
#define MONGOC_ERROR(...)
#define MONGOC_CRITICAL(...)
#define MONGOC_WARNING(...)
#define MONGOC_MESSAGE(...)
#define MONGOC_INFO(...)
#define MONGOC_DEBUG(...)
typedef void (*mongoc_log_func_t) (mongoc_log_level_t log_level,
                                   const char *log_domain,
                                   const char *message,
                                   void *user_data);
void
mongoc_log_set_handler (mongoc_log_func_t log_func, void *user_data);
void
mongoc_log (mongoc_log_level_t log_level,
            const char *log_domain,
            const char *format,
            ...);
const char *
mongoc_log_level_str (mongoc_log_level_t log_level);
void
mongoc_log_default_handler (mongoc_log_level_t log_level,
                            const char *log_domain,
                            const char *message,
                            void *user_data);
void
mongoc_log_trace_enable (void);
void
mongoc_log_trace_disable (void);
```

This abstraction can be used for logging in your application, or you can integrate the driver with an existing logging system.

## MACROS

To make logging a little less painful, various helper macros are provided. See the following example.

```
#undef MONGOC_LOG_DOMAIN
#define MONGOC_LOG_DOMAIN "my-custom-domain"
MONGOC_WARNING ("An error occurred: %s", strerror (errno));
```

## CUSTOM LOG HANDLERS

The default log handler prints a timestamp and the log message to **stdout**, or to **stderr** for warnings, critical messages, and errors. You can override the handler with **mongoc\_log\_set\_handler()**. Your handler function is called in a mutex for thread safety.

For example, you could register a custom handler to suppress messages at INFO level and below:

```
void
my_logger (mongoc_log_level_t log_level,
           const char *log_domain,
           const char *message,
           void *user_data)
{
   /* smaller values are more important */
   if (log_level < MONGOC_LOG_LEVEL_INFO) {
      mongoc_log_default_handler (log_level, log_domain, message, user_data);
   }
}
int
main (int argc, char *argv[])
{
   mongoc_log_set_handler (my_logger, NULL);
   mongoc_init ();
   /* ... your code ...  */
   mongoc_cleanup ();
   return 0;
}
```

Note that in the example above **mongoc\_log\_set\_handler()** is called before **mongoc\_init()**. Otherwise, some log traces could not be processed by the log handler.

To restore the default handler:

```
mongoc_log_set_handler (mongoc_log_default_handler, NULL);
```

## DISABLE LOGGING

To disable all logging, including warnings, critical messages and errors, provide an empty log handler:

```
mongoc_log_set_handler (NULL, NULL);
```

## TRACING

If compiling your own copy of the MongoDB C driver, consider configuring with **-DENABLE\_TRACING=ON** to enable function tracing and hex dumps of network packets to **STDERR** and **STDOUT** during development and debugging.

This is especially useful when debugging what may be going on internally in the driver.

Trace messages can be enabled and disabled by calling **mongoc\_log\_trace\_enable()** and **mongoc\_log\_trace\_disable()**

**NOTE:**

Compiling the driver with **-DENABLE\_TRACING=ON** will affect its performance. Disabling tracing with **mongoc\_log\_trace\_disable()** significantly reduces the overhead, but cannot remove it completely.

## AUTHOR

MongoDB, Inc

## COPYRIGHT

2009-present, MongoDB, Inc.