如何从共享库中调用函数？

发布于 2024-08-26 23:04:10 字数 490 浏览 10 评论 0原文

从共享库/dll 调用函数的最简单、最安全的方法是什么？我最感兴趣的是在linux上做这件事，但如果有一种独立于平台的方式那就更好了。

有人可以提供示例代码来展示如何进行以下工作，其中用户将自己的 foo 版本编译到共享库中吗？

// function prototype, implementation loaded at runtime:
std::string foo(const std::string);

int main(int argc, char** argv) {
  LoadLibrary(argv[1]); // loads library implementing foo
  std::cout << "Result: " << foo("test");
  return 0;
}

顺便说一句，我知道如何编译共享库（foo.so），我只需要知道一种在运行时加载它的简单方法。

原文

What is the easiest and safest way to call a function from a shared library / dll? I am mostly interested in doing this on linux, but it would be better if there were a platform-independent way.

Could someone provide example code to show how to make the following work, where the user has compiled his own version of foo into a shared library?

// function prototype, implementation loaded at runtime:
std::string foo(const std::string);

int main(int argc, char** argv) {
  LoadLibrary(argv[1]); // loads library implementing foo
  std::cout << "Result: " << foo("test");
  return 0;
}

BTW, I know how to compile the shared lib (foo.so), I just need to know an easy way to load it at runtime.

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思慕 2024-09-02 23:04:11

注意：您正在围绕库调用传递 C++ 对象（在本例中为 STL 字符串）。此级别没有标准 C++ ABI，因此要么尝试避免传递 C++ 对象，或者确保您的库和程序都是使用相同的编译器构建的（最好是同一台机器上的相同编译器，以避免任何与配置相关的微妙意外。）

不要忘记声明您导出的方法 extern "C"< /a> 在你的库代码中。

上面已经说过了，这里是一些实现您所说的想要实现的目标的代码：

typedef std::string (*foo_t)(const std::string);
foo_t foo = NULL;

...

# ifdef _WIN32
  HMODULE hDLL = ::LoadLibrary(szMyLib);
  if (!hDll) { /*error*/ }
  foo = (foo_t)::GetProcAddress(hDLL, "foo");
# else
  void *pLib = ::dlopen(szMyLib, RTLD_LAZY);
  if (!pLib) { /*error*/ }
  foo = (foo_t)::dlsym(pLib, "foo");
# endif
  if (!foo) { /*error*/ }

  ...

  foo("bar");

  ...

# ifdef _WIN32
  ::FreeLibrary(hDLL);
# else
  ::dlclose(pLib);
# endif

您可以进一步抽象：

#ifdef _WIN32
#include <windows.h>
typedef HANDLE my_lib_t;
#else
#include <dlfcn.h>
typedef void* my_lib_t;
#endif

my_lib_t MyLoadLib(const char* szMyLib) {
# ifdef _WIN32
  return ::LoadLibraryA(szMyLib);
# else //_WIN32
  return ::dlopen(szMyLib, RTLD_LAZY);
# endif //_WIN32
}

void MyUnloadLib(my_lib_t hMyLib) {
# ifdef _WIN32
  return ::FreeLibrary(hMyLib);
# else //_WIN32
  return ::dlclose(hMyLib);
# endif //_WIN32
}

void* MyLoadProc(my_lib_t hMyLib, const char* szMyProc) {
# ifdef _WIN32
  return ::GetProcAddress(hMyLib, szMyProc);
# else //_WIN32
  return ::dlsym(hMyLib, szMyProc);
# endif //_WIN32
}

typedef std::string (*foo_t)(const std::string);
typedef int (*bar_t)(int);
my_lib_t hMyLib = NULL;
foo_t foo = NULL;
bar_t bar = NULL;

...

  if (!(hMyLib = ::MyLoadLib(szMyLib)) { /*error*/ }
  if (!(foo = (foo_t)::MyLoadProc(hMyLib, "foo")) { /*error*/ }
  if (!(bar = (bar_t)::MyLoadProc(hMyLib, "bar")) { /*error*/ }

  ...

  foo("bar");
  bar(7);

  ...

  ::MyUnloadLib(hMyLib);

NOTE: You are passing C++ objects (in this case STL strings) around library calls. There is no standard C++ ABI at this level, so either try to avoid passing C++ objects around, or ensure that both your library and your program have been built with the same compiler (ideally the same compiler on the same machine, to avoid any subtle configuration-related surprises.)

Do not forget to declare your exported methods extern "C" inside your library code.

The above having been said, here is some code implementing what you said you want to achieve:

typedef std::string (*foo_t)(const std::string);
foo_t foo = NULL;

...

# ifdef _WIN32
  HMODULE hDLL = ::LoadLibrary(szMyLib);
  if (!hDll) { /*error*/ }
  foo = (foo_t)::GetProcAddress(hDLL, "foo");
# else
  void *pLib = ::dlopen(szMyLib, RTLD_LAZY);
  if (!pLib) { /*error*/ }
  foo = (foo_t)::dlsym(pLib, "foo");
# endif
  if (!foo) { /*error*/ }

  ...

  foo("bar");

  ...

# ifdef _WIN32
  ::FreeLibrary(hDLL);
# else
  ::dlclose(pLib);
# endif

You can abstract this further:

#ifdef _WIN32
#include <windows.h>
typedef HANDLE my_lib_t;
#else
#include <dlfcn.h>
typedef void* my_lib_t;
#endif

my_lib_t MyLoadLib(const char* szMyLib) {
# ifdef _WIN32
  return ::LoadLibraryA(szMyLib);
# else //_WIN32
  return ::dlopen(szMyLib, RTLD_LAZY);
# endif //_WIN32
}

void MyUnloadLib(my_lib_t hMyLib) {
# ifdef _WIN32
  return ::FreeLibrary(hMyLib);
# else //_WIN32
  return ::dlclose(hMyLib);
# endif //_WIN32
}

void* MyLoadProc(my_lib_t hMyLib, const char* szMyProc) {
# ifdef _WIN32
  return ::GetProcAddress(hMyLib, szMyProc);
# else //_WIN32
  return ::dlsym(hMyLib, szMyProc);
# endif //_WIN32
}

typedef std::string (*foo_t)(const std::string);
typedef int (*bar_t)(int);
my_lib_t hMyLib = NULL;
foo_t foo = NULL;
bar_t bar = NULL;

...

  if (!(hMyLib = ::MyLoadLib(szMyLib)) { /*error*/ }
  if (!(foo = (foo_t)::MyLoadProc(hMyLib, "foo")) { /*error*/ }
  if (!(bar = (bar_t)::MyLoadProc(hMyLib, "bar")) { /*error*/ }

  ...

  foo("bar");
  bar(7);

  ...

  ::MyUnloadLib(hMyLib);

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海夕 2024-09-02 23:04:11

LoadLibrary 是一个用于加载 DLL 的 Windows 函数。您可以使用 GetProcAddress 检查符号是否存在。在 Linux/Unix 上，您需要 dlopen/dlsym。要在跨平台中执行此操作，您可以编写一个函数，使用预处理器调用这些方法中的任何一个，因此，类似于：

int loadlibrary(char* library)
{
#ifdef _WIN32
    /* do windows code */

#endif
#ifdef _LINUX
    /* do linux code */

#endif
}

这是实现此类事情的一种方法。您还可以通过在自己的源代码树中包含不同的标头来实现特定平台的函数实现。这可能是一个更好的方法。无论哪种情况，我们的想法都是从底层 API 中进行抽象。

LoadLibrary is a Windows function for loading DLLs. You can check for symbol existence with GetProcAddress. On Linux/Unix you want dlopen/dlsym. To do this in cross platform, you could write a function that calls either of these methods using pre-processor, so, something like:

int loadlibrary(char* library)
{
#ifdef _WIN32
    /* do windows code */

#endif
#ifdef _LINUX
    /* do linux code */

#endif
}

This is one way to achieve this sort of thing. You could also do it by including a different header in your own source tree for specific platform implementations of functions. This is probably a better way. In either case the idea is to abstract from the underlying API.

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