---
title: os_log_create
framework: os
role: symbol
role_heading: Function
path: os/os_log_create
---

# os_log_create

Creates a custom log object.

## Declaration

```occ
extern os_log_tos_log_create(const char *subsystem, const char *category);
```

## Parameters

- `subsystem`: An identifier string, in reverse DNS notation, that represents the subsystem that’s performing logging, for example, com.your_company.your_subsystem_name. The subsystem is used for categorization and filtering of related log messages, as well as for grouping related logging settings.
- `category`: A category within the specified subsystem. The system uses the category to categorize and filter related log messages, as well as to group related logging settings within the subsystem’s settings. A category’s logging settings override those of the parent subsystem.

## Return Value

Return Value A value of type os_log_t, which can be passed to other logging functions to perform logging and to determine whether a specific level of logging is enabled. A value is always returned and should be released when no longer needed.

## Discussion

Discussion Typically, use the OS_LOG_DEFAULT constant to perform logging using the system’s behavior. Create a custom log object only when you want to tag messages with a specific subsystem and category for the purpose of filtering, or to customize the logging behavior of your subsystem with a profile for debugging purposes. You only need to call this function once to initialize a custom log object. It doesn’t need to be called again when changing logging settings. The system automatically detects changes to logging settings.

## See Also

### Related Documentation

- [isEnabled(type:)](os/oslog/isenabled(type:).md)