Android logcat系统

一 .logcat命令介绍

android log系统:

logcat介绍 :

logcat是android中的一个命令行工具，可以用于得到程序的log信息.

二.C/C++logcat访问接口

Android系统中的C/C++日志接口是通过宏来使用的。在system/core/include/android/log.h定义了日志的级别：

/*
 * Android log priority values, in ascending priority order.
 */
typedef enum android_LogPriority {
	ANDROID_LOG_UNKNOWN = 0,
	ANDROID_LOG_DEFAULT,	/* only for SetMinPriority() */
	ANDROID_LOG_VERBOSE,
	ANDROID_LOG_DEBUG,
	ANDROID_LOG_INFO,
	ANDROID_LOG_WARN,
	ANDROID_LOG_ERROR,
	ANDROID_LOG_FATAL,
	ANDROID_LOG_SILENT,	/* only for SetMinPriority(); must be last */
} android_LogPriority;

在system/core/include/cutils/log.h中，定义了对应的宏，如对应于ANDROID_LOG_VERBOSE的宏LOGV：

/*
 * This is the local tag used for the following simplified
 * logging macros. You can change this preprocessor definition
 * before using the other macros to change the tag.
 */
#ifndef LOG_TAG
#define LOG_TAG NULL
#endif
 
/*
 * Simplified macro to send a verbose log message using the current LOG_TAG.
 */
#ifndef LOGV
#if LOG_NDEBUG
#define LOGV(...)   ((void)0)
#else
#define LOGV(...)   ((void)LOG(LOG_VERBOSE, LOG_TAG, __VA_ARGS__))
#endif
#endif
 
/*
 * Basic log message macro.
 *
 * Example:
 *  LOG(LOG_WARN, NULL, "Failed with error %d", errno);
 *
 * The second argument may be NULL or "" to indicate the "global" tag.
 */
#ifndef LOG
#define LOG(priority, tag, ...) \
     LOG_PRI(ANDROID_##priority, tag, __VA_ARGS__)
#endif
 
/*
 * Log macro that allows you to specify a number for priority.
 */
#ifndef LOG_PRI
#define LOG_PRI(priority, tag, ...) \
     android_printLog(priority, tag, __VA_ARGS__)
#endif
 
/*
 * ================================================================
 *
 * The stuff in the rest of this file should not be used directly.
 */
#define android_printLog(prio, tag, fmt...) \
     __android_log_print(prio, tag, fmt)

  因此，如果要使用C/C++日志接口，只要定义自己的LOG_TAG宏和包含头文件system/core/include/cutils/log.h就可以了：

 #define LOG_TAG "MY LOG TAG"

         #include <cutils/log.h>

         就可以了，例如使用LOGV：

         LOGV("This is the log printed by LOGV in android user space.");

三.Java logcat访问接口

Android系统在Frameworks层中定义了Log接口（frameworks/base/core/java/android/util/Log.java）：

................................................
 
public final class Log {
 
................................................
 
	/**
	 * Priority constant for the println method; use Log.v.
         */
	public static final int VERBOSE = 2;
 
	/**
	 * Priority constant for the println method; use Log.d.
         */
	public static final int DEBUG = 3;
 
	/**
	 * Priority constant for the println method; use Log.i.
         */
	public static final int INFO = 4;
 
	/**
	 * Priority constant for the println method; use Log.w.
         */
	public static final int WARN = 5;
 
	/**
	 * Priority constant for the println method; use Log.e.
         */
	public static final int ERROR = 6;
 
	/**
	 * Priority constant for the println method.
         */
	public static final int ASSERT = 7;
 
.....................................................
 
	public static int v(String tag, String msg) {
		return println_native(LOG_ID_MAIN, VERBOSE, tag, msg);
	}
 
	public static int v(String tag, String msg, Throwable tr) {
		return println_native(LOG_ID_MAIN, VERBOSE, tag, msg + '\n' + getStackTraceString(tr));
	}
 
	public static int d(String tag, String msg) {
		return println_native(LOG_ID_MAIN, DEBUG, tag, msg);
	}
 
	public static int d(String tag, String msg, Throwable tr) {
		return println_native(LOG_ID_MAIN, DEBUG, tag, msg + '\n' + getStackTraceString(tr));
	}
 
	public static int i(String tag, String msg) {
		return println_native(LOG_ID_MAIN, INFO, tag, msg);
	}
 
	public static int i(String tag, String msg, Throwable tr) {
		return println_native(LOG_ID_MAIN, INFO, tag, msg + '\n' + getStackTraceString(tr));
	}
 
	public static int w(String tag, String msg) {
		return println_native(LOG_ID_MAIN, WARN, tag, msg);
	}
 
	public static int w(String tag, String msg, Throwable tr) {
		return println_native(LOG_ID_MAIN, WARN, tag, msg + '\n' + getStackTraceString(tr));
	}
 
	public static int w(String tag, Throwable tr) {
		return println_native(LOG_ID_MAIN, WARN, tag, getStackTraceString(tr));
	}
	
	public static int e(String tag, String msg) {
		return println_native(LOG_ID_MAIN, ERROR, tag, msg);
	}
 
	public static int e(String tag, String msg, Throwable tr) {
		return println_native(LOG_ID_MAIN, ERROR, tag, msg + '\n' + getStackTraceString(tr));
	}
 
..................................................................
 
	/**@hide */ public static native int println_native(int bufID,
		int priority, String tag, String msg);
}

因此，如果要使用Java日志接口，只要在类中定义的LOG_TAG常量和引用android.util.Log就可以了：

        private static final String LOG_TAG = "MY_LOG_TAG";

        Log.i(LOG_TAG, "This is the log printed by Log.i in android user space.");

四.logcat命令参数

//将缓冲区的log打印到屏幕并退出
 
adb logcat -d
 
//清除缓冲区log（testCase运行前可以先清除一下）
 
adb logcat -c
 
//打印缓冲区大小并退出
 
adb logcat -g
 
//输出log
 
adb logcat -f /data/local/tmp/log.txt -n 10 -r 1