Since It's pretty hard to debug native android code, I'm going to the "printf trace" approach.
So, my question is, in a native code, wheres the standards "printf("something")" appears when running a Android application?
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possible duplicate of [How to see printf lines in gdb?](http://stackoverflow.com/questions/5459324/how-to-see-printf-lines-in-gdb) – richq Jun 21 '11 at 18:34
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Possible duplicate of [Is "std::cout" usable in Android-ndk](https://stackoverflow.com/questions/8870174/is-stdcout-usable-in-android-ndk) – Ciro Santilli OurBigBook.com Nov 06 '17 at 09:40
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My question was from one year before @CiroSantilli刘晓波死六四事件法轮功 – Marcos Vasconcelos Nov 06 '17 at 13:39
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Hi Marcos, the current consensus is to close by "quality": http://meta.stackexchange.com/questions/147643/should-i-vote-to-close-a-duplicate-question-even-though-its-much-newer-and-ha Since "quality" is not measurable, I just go by upvotes. ;-) Likely it comes down to which question hit the best newbie Google keywords on the title. – Ciro Santilli OurBigBook.com Nov 06 '17 at 15:10
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Not willing to improve the question quality though? The other question is about the physical space where the log appears to, I'm asking how to see in logcat. – Marcos Vasconcelos Nov 06 '17 at 15:18
2 Answers
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Log to logcat.
1) To invoke the logger in native code include the header and call _android_log_write(..).
#include <android/log.h>
__android_log_write(ANDROID_LOG_INFO, "tag here", "message here");
2) In your Android.mk file include the log lib like this.
LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog
Ryan Reeves
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perfect ! On a side note, this works even without editing the .mk on my test case. – johan d Mar 29 '14 at 19:10
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1In my case `LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog` didn't work. I had to use `LOCAL_SHARED_LIBRARIES := liblog` instead. – gfrigon Mar 31 '15 at 01:02
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There are shorter macros available in order to log to logcat.
#define LOG_TAG "my_log_tag"
#include <cutils/log.h>
ALOGD("Format this %d", some_int);
In Android.mk, add the liblog library to LOCAL_SHARED_LIBRARIES when building in 'mydroid' (full android system build). In case of ndk build LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog can be used.
include $(CLEAR_VARS)
LOCAL_MODULE := foo
LOCAL_SRC_FILES := foo.c
# if mydroid
LOCAL_SHARED_LIBRARIES := liblog
# in ndk, use LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog instead
include $(BUILD_EXECUTABLE)
There are various other macros defined for all levels of logging. From cutils/log.h:
#define ALOGV(...) ((void)ALOG(LOG_VERBOSE, LOG_TAG, __VA_ARGS__))
#define ALOGD(...) ((void)ALOG(LOG_DEBUG, LOG_TAG, __VA_ARGS__))
...
#define ALOGE(...) ((void)ALOG(LOG_ERROR, LOG_TAG, __VA_ARGS__))
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I did all the above suggestions. but, i still get undefined reference to '__android_log_write'. Any new solutions? – Androidification Jul 23 '20 at 15:26