harmony 鸿蒙HiLog Development (Native)

2023-02-03
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HiLog Development (Native)

Overview

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.

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. Input arguments: See Parameter Description. Output arguments: None Return value: total number of bytes if log printing is successful; -1 otherwise.
#define OH_LOG_DEBUG(type, …) ((void)OH_LOG_Print((type), LOG_DEBUG, LOG_DOMAIN, LOG_TAG, _VAARGS__))	Outputs DEBUG logs. This is a function-like macro.
#define OH_LOG_INFO(type, …) ((void)OH_LOG_Print((type), LOG_INFO, LOG_DOMAIN, LOG_TAG, _VAARGS__))	Outputs INFO logs. This is a function-like macro.
#define OH_LOG_WARN(type, …) ((void)OH_LOG_Print((type), LOG_WARN, LOG_DOMAIN, LOG_TAG, _VAARGS__))	Outputs WARN logs. This is a function-like macro.
#define OH_LOG_ERROR(type, …) ((void)OH_LOG_Print((type), LOG_ERROR, LOG_DOMAIN, LOG_TAG, _VAARGS__))	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, _VAARGS__))	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. Input arguments: See Parameter Description. Output arguments: none Return value: true if the specified logs can be printed; false otherwise.

Parameter Description

Name	Type	Mandatory	Description
type	enum	Yes	Log printing type. The default value is LOG_APP for application logs.
level	enum	Yes	Log printing level. For details, see Log Level.
domain	number	Yes	Service domain of logs. The value ranges from 0x0 to 0xFFFF. You can define the value as required.
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. 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
DEBUG	3	Log level used to record more detailed process information than INFO logs to help developers analyze service processes and locate faults.
INFO	4	Log level used to record key service process nodes and exceptions that occur during service running as well as information about unexpected exceptions, such as network signal loss and login failure. These logs should be recorded by the dominant module in the service to avoid repeated logging conducted by multiple invoked modules or low-level functions.
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 Example

Add the link of libhilog_ndk.z.so to CMakeLists.txt: target_link_libraries(entry PUBLIC libhilog_ndk.z.so)
Include the hilog header file in the source file, and define the domain and tag macros. c++ #include "hilog/log.h"

#undef LOG_DOMAIN
#undef LOG_TAG
#define LOG_DOMAIN 0x3200 // Global domain, which identifies the service domain.
#define LOG_TAG "MY_TAG" // Global tag, which identifies the module log tag.

Print logs. For example, to print ERROR logs, use the following code: c++ OH_LOG_ERROR(LOG_APP, "Failed to visit %{private}s, reason:%{public}d.", url, errno);
View the output log information. 12-11 12:21:47.579 2695 2695 E A03200/MY_TAG: Failed to visit <private>, reason:11.