Build dynamic native c code for android ? Left or Right

Build dynamic native c++ code for android

在另外一个帖子Native Hello World on Android中，neil已经介绍了如何编译一个静态的native程序在Android中运行，本文主要说明如何编译动态链编的native程序。

编译环境要求：下载Android的源码，并执行完一次完整的编译。以下的所有命令均是在编译后的源码根目录下执行。

1. 编译C code
同样以hello.c为例：

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代码:

#include <stdio.h>
#include <stdlib.h>

int main()
{
printf("hello, world!\n");
return 0;
}

执行以下步骤生成动态链编的binary文件：

• 生成目标文件：prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/arm-eabi- gcc -I bionic/libc/arch-arm/include -I bionic/libc/include -I bionic/libstdc++/include -I bionic/libc/kernel/common -I bionic/libc/kernel/arch-arm -include system/core/include/arch/linux-arm/AndroidConfig.h -c -o hello.o hello.c
• 生 成可执行程序：prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/arm-eabi-gcc -nostdlib -Bdynamic -Wl,-T,build/core/armelf.x -Wl,-dynamic-linker,/system/bin/linker -Wl,–gc-sections -Wl,-z,nocopyreloc -o hello -Lout/target/product/generic/obj/lib -Wl,-rpath-link=out/target/product/generic/obj/lib -lc -lstdc++  out/target/product/generic/obj/lib/crtbegin_dynamic.o hello.o -Wl,–no-undefined ./prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/../lib/gcc/arm-eabi/4.2.1/interwork/libgcc.a out/target/product/generic/obj/lib/crtend_android.o

用命令file查看生成的hello文件属性：
hello: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), stripped
可以证明此时的hello是一个动态链编的文件。

2. 编译native c++ 代码
以hello_cpp为例：

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代码:

hello_cpp.h
#ifndef HELLO_CPP_H
#define HELLO_CPP_H

class Hello
{
public:
Hello();
~Hello();
void printMessage(char* msg);
};

#endif

hello_cpp.cpp
#include <stdio.h>
#include "hello_cpp.h"

Hello::Hello()
{
}

Hello::~Hello()
{
}

void Hello::printMessage(char* msg)
{
printf("C++ example printing message: %s", msg);
}

int main(void)
{
Hello hello_obj;
hello_obj.printMessage("Hello world!\n");
return 0;
}

执行以下命令完成：

• 编译目标文件：prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/arm-eabi- g++ -I bionic/libc/arch-arm/include -I bionic/libc/include -I bionic/libstdc++/include -I bionic/libc/kernel/common -I bionic/libc/kernel/arch-arm -include system/core/include/arch/linux-arm/AndroidConfig.h -fno-exceptions -fno-rtti -c  -o hello_cpp.o hello_cpp.cpp
• 编译可执行程 序：prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/arm-eabi-g++ -nostdlib -Bdynamic -Wl,-T,build/core/armelf.x -Wl,-dynamic-linker,/system/bin/linker -Wl,–gc-sections -Wl,-z,nocopyreloc -o hello_cpp -Lout/target/product/generic/obj/lib -Wl,-rpath-link=out/target/product/generic/obj/lib -lc -lstdc++  out/target/product/generic/obj/lib/crtbegin_dynamic.o hello_cpp.o -Wl,–no-undefined ./prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/../lib/gcc/arm-eabi/4.2.1/interwork/libgcc.a out/target/product/generic/obj/lib/crtend_android.o

同样用file查看hello_cpp的文件属性：
hello_cpp: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), stripped

但是很不幸的是，android自带的toolchain不支持C++标准库的开发，即所有的std namespace下的类均无法使用，包括基本的string。

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