如何创建具有高可维护性的共享库? [英] how to create a shared object with high maintainability?
本文介绍了如何创建具有高可维护性的共享库?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我尝试为C ++项目创建一个共享对象，其目的是:每次我想带来一个新类时，我都只重新编译共享对象.
I try to create a shared object for my C++ project with the purpose: every time I want to bring a new class, I recompile shared object only.
下面是测试代码:
test.h:
#if !defined(_TEST_)
#define _TEST_
#include <string>
#include <memory>
class Test {
private:
public:
Test() {
}
~Test() {
}
virtual void show(const std::string &) = 0;
};
#ifdef __cplusplus
extern "C" {
#endif
// std::shared_ptr<Test> getObject();
#ifdef __cplusplus
}
#endif
#endif // _TEST_
getObject.cpp:类TestSo从Test派生.
getObject.cpp: class TestSo derive from Test.
#include <memory>
#include "testso.h"
std::shared_ptr<Test> getObject()
{
return std::make_shared<TestSo>();
}
和main.cpp:
#include "test.h"
#include <dlfcn.h>
#include <string>
#include <memory>
std::shared_ptr<Test> (*getTestSo)();
int main(int argc, char const *argv[])
{
//...
void *handle = dlopen("/usr/lib/libfunc.so", RTLD_NOW);
if(handle == NULL)
return 1;
getTestSo = (std::shared_ptr<Test> (*)())dlsym(handle, "getObject");
const char *dlmsg = dlerror();
if(dlmsg != NULL) {
printf("dlsym: %s\n", dlmsg);
dlclose(handle);
return 1;
}
std::shared_ptr<Test> classSo = getTestSo();
classSo->show("Hi");
dlclose(handle);
//...
return 0;
}
我使用以下命令行编译代码:
arm-none-linux-gnueabi-g++ -std=c++11 -c -fPIC getObject.cpp
arm-none-linux-gnueabi-g++ -shared getObject.o -o libtest.so
arm-none-linux-gnueabi-g++ -std=c++11 -L./ main.cpp -o test -ldl -ltest
I compile code with the following command line:
arm-none-linux-gnueabi-g++ -std=c++11 -c -fPIC getObject.cpp
arm-none-linux-gnueabi-g++ -shared getObject.o -o libtest.so
arm-none-linux-gnueabi-g++ -std=c++11 -L./ main.cpp -o test -ldl -ltest
编译器没有给我任何警告或错误.它说我运行程序时undefined symbol: getObject.
compiler doesn't give me any warning or error. it says that undefined symbol: getObject when I run program.
最后，我发现我 必须 在test.h内的范围extern "C"中声明了getObject.
finally I find that I must declare getObject in scope extern "C" within test.h.
dlsym从libtest.so获取getObject的地址，程序将跳转到该地址.为什么我必须声明getObject?这违反了我的目的.或者，如果我完全走错了路，该怎么办?如果没有，我该如何解决?
dlsym fetch address of getObject from libtest.so and the program would jump to that address. why I must declare getObject? that is against my purpose. Or if I am totally going a wrong way, how do I do? if not, how can I fix it?
arm-none-linux-gnueabi-nm -D libfunc.so
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推荐答案
您的方法行不通，因为C ++会在编译过程中破坏名称，也许可以在网上或例如在
You approach does not work, because C++ mangles names during compilation, maybe more on this topic can be found over the net or for example in this thread. When you compile a function named std::shared_ptr<Test> getObject() it ends up as a symbol named _Z9getObjectv, so in you need to open this symbol dlsym(handle, "_Z9getObjectv");
每次我想带一个新类时，我只会重新编译共享对象.
every time I want to bring a new class, I recompile shared object only.
我不明白为什么您不希望仅链接到您的程序.创建dlsym是为了允许与链接程序有关的程序来处理加载，该功能似乎在您的程序中不需要.对于您的程序，只需添加该函数的前向声明(不带任何外部C，因为名称由C ++修饰):
I don't understand why do you don't want to just link against your program. dlsym was created to allow linker-related programs to handle the loading, the functionality seems not needed in your program. In case of your program simply adding a forward declaration of the function (without any extern C, because the name is mangled by C++):
std::shared_ptr<Test> getObject();
到您的test.h文件，然后使用:
to your test.h file and then compiling with:
-ltest
就像您现在所做的那样(！)将链接到共享库.这就是共享库首先存在的原因-因此您可以更改基础代码而无需更改客户端代码.同样，在链接的情况下，如果找不到符号，链接器将发出符号解析错误，因此您具有另一层保护，您不必担心名称混乱.只需将main.cpp更改为:
as you do now(!) will link against shared library. That's exactly the reason why shared libraries exists in the first place - so you can change the underlying code without changing the client code. Also in case of linking the linker will issue symbol resolution error if the symbol is not found, so you have another layer of protection and you don't have to worry about mangled names. Just change your main.cpp to:
#include "test.h"
#include <dlfcn.h>
#include <string>
#include <memory>
int main(int argc, char const *argv[])
{
std::shared_ptr<Test> getObject();
std::shared_ptr<Test> (*getTestSo)() = getObject;
std::shared_ptr<Test> classSo = getTestSo();
return 0;
}
它应该可以工作(具有正确的LD_LIBRARY_PATH)...
and it should work (with proper LD_LIBRARY_PATH)...
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