HiLog is the log system of OpenHarmony that provides logging for the system framework, services, and applications to record information on user operations and system running status.
> **NOTE**
> This development guide is applicable only when you use Native APIs for application development. For details about the APIs, see [HiLog Native API Reference](../reference/native-apis/_hi_log.md).
>
> This development guide is applicable only when you use Native APIs for application development. For details about the APIs, see [HiLog Native API Reference](https://gitee.com/openharmony-sig/interface_native_header/blob/master/en/native_sdk/dfx/log.h).
## Available APIs
| API/Macro| Description|
| -------- | -------- |
| int OH_LOG_Print(LogType type, LogLevel level, unsigned int domain, const char *tag, const char *fmt, ...) | Outputs logs based on the specified log type, log level, service domain, log tag, and variable parameters determined by the format specifier and privacy identifier in the printf format.<br>Input parameters: See [Parameter Description](#parameter-description).<br>Output parameters: None<br>Return value: total number of bytes if log printing is successful; **-1** otherwise.|
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@@ -14,6 +19,7 @@ HiLog is the log system of OpenHarmony that provides logging for the system fram
| #define OH_LOG_ERROR(type, ...) ((void)OH_LOG_Print((type), LOG_ERROR, LOG_DOMAIN, LOG_TAG, \_*VA*ARGS__)) | Outputs ERROR logs. This is a function-like macro.|
| #define OH_LOG_FATAL(type, ...) ((void)OH_LOG_Print((type), LOG_FATAL, LOG_DOMAIN, LOG_TAG, \_*VA*ARGS__)) | Outputs FATAL logs. This is a function-like macro.|
| bool OH_LOG_IsLoggable(unsigned int domain, const char *tag, LogLevel level) | Checks whether logs of the specified service domain, tag, and level can be printed.<br>Input parameters: See [Parameter Description](#parameter-description).<br>Output arguments: none<br>Return value: **true** if the specified logs can be printed; **false** otherwise.|
## Parameter Description
| Name| Type | Mandatory| Description |
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@@ -24,7 +30,9 @@ HiLog is the log system of OpenHarmony that provides logging for the system fram
| tag | string | Yes | Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.|
| fmt | string | Yes | Format string used to output logs in a specified format. It can contain several parameters, where the parameter type and privacy identifier are mandatory.<br>Parameters labeled **{public}** are public data and are displayed in plaintext; parameters labeled **{private}** (default value) are private data and are filtered by **\<private>**.|
| args | any[] | Yes | Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.|
## LogLevel
Log level.
| Name | Value | Description |
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@@ -34,7 +42,9 @@ Log level.
| WARN | 5 | Log level used to record severe, unexpected faults that have little impact on users and can be rectified by the programs themselves or through simple operations.|
| ERROR | 6 | Log level used to record program or functional errors that affect the normal running or use of the functionality and can be fixed at a high cost, for example, by resetting data.|
| FATAL | 7 | Log level used to record program or functionality crashes that cannot be rectified.
## Development Examples
1. Add the link of **libhilog_ndk.z.so** to **CMakeLists.txt**:
```
target_link_libraries(entry PUBLIC libhilog_ndk.z.so)
