CODEWITHSUNDEEP
c++android-ndkgnuvisualgdb
user3416447
user3416447

Reputation: 131

What is the difference between gnustl_shared and gnustl_static in Android NDK library .a file?

I want to create android library using c++ stl.

my build tools are visual studio 2015, Visual GDB.

source code is

.cpp

#include <jni.h>
#include "AndroidProject2.h"
#include <vector>
void foo() { std::vector<int> aaa; aaa.push_back(1); }

Android.mk

# Generated by VisualGDB
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE    := AndroidProject2-shared
LOCAL_SRC_FILES := AndroidProject2.cpp
COMMON_SRC_FILES := $(LOCAL_SRC_FILES)
include $(BUILD_SHARED_LIBRARY)

include $(CLEAR_VARS)
LOCAL_MODULE    := AndroidProject2-static
LOCAL_SRC_FILES :=  $(COMMON_SRC_FILES)
include $(BUILD_STATIC_LIBRARY)

Application.mk

APP_MODULES := AndroidProject2-static AndroidProject2-shared
APP_ABI := all
APP_STL := gnustl_static
NDK_TOOLCHAIN_VERSION :=4.9

I succeed build, so, created lib files libAndroidProject2-static.a, libAndroidProject2-static.so

than, I try to change APP_STL option in Application.mk

APP_MODULES := AndroidProject2-static AndroidProject2-shared
APP_ABI := all
APP_STL := gnustl_shared
NDK_TOOLCHAIN_VERSION :=4.9

surely, succeed build. so, created lib files libAndroidProject2-shared.a, libAndroidProject2-shared.so

than, I Compare it and previous build outputs.

I Found the difference about .so file. gnustl_static option's .so file is more bigger than gnustl_shared option's it. but .a is same.

why? I used nm, readelf but can't find difference. what is diff???

Upvotes: 2

Views: 6010

Answers (2)

Dan Albert
Dan Albert

Reputation: 10509

There are two questions here:

Why does using gnustl_static make larger shared libraries than gnustl_shared?

When you use a static library you're including code from that library directly into your shared library, so your library grows. When you use a shared library you load the code that would have been included from the other shared library instead of including it. The size you need to compare is libAndroidProject2-static.so + libgnustl_shared.so, since both must be present at runtime.

Why didn't using gnustl_static make a larger static library?

Static libraries (libAndroidProject2-static.a, in this case) aren't linked; they're just archives of the compiled sources. libgnustl_static.a doesn't get included until you actually link libAndroidProject-static.a into something, at which point you'll also need to link libgnustl_static.a.

You'd see the size difference when you linked libAndroidProject2-static.a (and libgnustl_static.a) into a shared library or exeuctable.

Upvotes: 2

V-master
V-master

Reputation: 2177

The difference is that when you use static, the code of std is compiled into resulting .so file, while using shared, resulting so file requires to have std in separate so file

Upvotes: 0

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