blocks|key|489892|text|对于Linux/POSIX，您可以使用dlopen()系列函数在运行时加载共享库、查找符号地址等。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|489893|如果您想添加库依赖项以使处理可加载代码变得更容易(更可移植)，请查看glib的module+API。|489894|entityMap|0|LINK|mutability|MUTABLE|url|http://linux.die.net/man/3/dlopen|1|http://library.gnome.org/devel/glib/stable/glib-Dynamic-Loading-of-Modules.html^0|J|8|J|8|0|0|13|A|1|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@$9|U|A|V|1|W]]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@$9|Y|A|Z|1|10]]|E|$]]|$1|H|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]|P|$5|K|L|M|E|$N|Q]]]]

For Linux/POSIX, you use the <code><a href="http://linux.die.net/man/3/dlopen" rel="nofollow noreferrer">dlopen()</a></code> family of functions to load shared libraries at runtime, look up symbol addresses, and so on.

If you want to add a library dependency to make working with loadable code a bit easier (and more portable), look into glib's <a href="http://library.gnome.org/devel/glib/stable/glib-Dynamic-Loading-of-Modules.html" rel="nofollow noreferrer">module API</a>.

blocks|key|489547|text|您可能希望了解一下dlopen、dlsym和类似的函数。它们可以在POSIX+(linux、OSX、win32%2Bcygwin等)上工作。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|489548|使用dlopen()，您可以打开一个共享库。您的LoadSharedLibrary可以是dlopen()的包装器。GetFuncPtr()函数可以是dlsym()的包装器。你能做的就是围绕dl*()函数编写代码，让它变得健壮，就像做一些错误检查一样。您可能还想在共享库中定义一个接口，即“导出”支持的函数的结构。通过这种方式，您可以获得方法列表，而无需借助读取elf文件。|489549|还有a+nice+page+about+function+pointers+in+C+and+C%2B%2B。|489550|这里有一个关于用法的快速示例：|489551|void*+LoadSharedLibrary(const+char*+name)
{
+++return+dlopen(name,+RTLD_LOCAL+%7C+RTLD_LAZY);
}++++

void*+GetFunctionAddress(void*+h,+const+char*+name)
{
+++return+dlsym(h,+name);
}

const+char**+GetFunctionList(void*+h)
{
+++return+(char**)dlsym(h,+"ExportedFunctions");
}

//+Declare+a+variable+to+hold+the+function+pointer+we+are+going+to+retrieve.
//+This+function+returns+nothing+(first+void)+and+takes+no+parameters+(second+void).
//+The+*+means+we+want+a+pointer+to+a+function.
void+(*doStuff)(void);

//+Here+we+retrieve+the+function+pointer+from+the+dl.
doStuff+=+GetFunctionAddress(h,+"doStuff");

//+And+this+how+we+call+it.+It+is+a+convention+to+call+function+pointers+like+this.
//+But+you+can+read+it+as+'take+contents+of+the+doStuff+var+and+call+that+function'.
(*doStuff)();|code-block|syntax|javascript|489552|entityMap|0|LINK|mutability|MUTABLE|url|http://manpages.ubuntu.com/manpages/hardy/man3/dlopen.3.html|1|http://www.newty.de/fpt/index.html^0|9|6|0|0|0|2|1C|1|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|6|7|12|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|13|8|@]|9|@$A|14|B|15|1|16]]|C|$]]|$1|H|3|I|5|6|7|17|8|@]|9|@]|C|$]]|$1|J|3|K|5|L|7|18|8|@]|9|@]|C|$M|N]]|$1|O|3|-4|5|6|7|19|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]|W|$5|R|S|T|C|$U|X]]]]

You might want to have a look at the <a href="http://manpages.ubuntu.com/manpages/hardy/man3/dlopen.3.html" rel="nofollow noreferrer">dlopen</a>, dlsym and similar functions. These work on POSIX (linux, OSX, win32+cygwin etc...).

With dlopen(), you can open a shared library. Your LoadSharedLibrary can be a wrapper around dlopen(). You GetFuncPtr() function can be a wrapper around dlsym(). What you can do is write code around the dl*() functions to make it robust - like do some error checking. You also might want to define an interface in the shared library, i.e. a struct that 'exports' supported functions. This way you can get a list of methods without the need to resorting to reading elf files.

There is also <a href="http://www.newty.de/fpt/index.html" rel="nofollow noreferrer">a nice page about function pointers in C and C++</a>.

Here's a quick example on the usage:

<pre><code>void* LoadSharedLibrary(const char* name)
{
 return dlopen(name, RTLD_LOCAL | RTLD_LAZY);
} 

void* GetFunctionAddress(void* h, const char* name)
{
 return dlsym(h, name);
}

const char** GetFunctionList(void* h)
{
 return (char**)dlsym(h, "ExportedFunctions");
}

// Declare a variable to hold the function pointer we are going to retrieve.
// This function returns nothing (first void) and takes no parameters (second void).
// The * means we want a pointer to a function.
void (*doStuff)(void);

// Here we retrieve the function pointer from the dl.
doStuff = GetFunctionAddress(h, "doStuff");

// And this how we call it. It is a convention to call function pointers like this.
// But you can read it as 'take contents of the doStuff var and call that function'.
(*doStuff)();
</code></pre>

blocks|key|1789120|text|使用dlopen/dlsym，并使用-fPIC+/+FPIC代码编译它|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1789121|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

use dlopen/dlsym as well as compile it with -fPIC / FPIC code

I am working with a legacy C library that can be extended by writing user defined function(s) and then recompiling the source. I want to avoid the compilation requirement, and instead extend it ONCE with a function (see pseudocode below):

This function will be implemented like this:

<pre><code>VARIANT_TYPE CallSharedLibFunction(const char* library_name, const char* funcname, const char *params, const char* return_type){
// parse arguments and get data types and count
// initiate variable of data type indicated by return_type, to hold returned variable

/* this is the part I need help with */
// lptr = LoadSharedLibrary(library_name);
// funcptr = GetFunctionAddress(lptr, funcname);

// call function and pass it arguments
retvalue = funcptr(param1, param2, param3);

// wrap up returned value in the VARIANT_TYPE
VARIANT_TYPE ret;
setVariantValue(ret, retvalue, return_type);

return ret;
</code></pre>

} 

Note: despite the "Windows sounding" names (VARIANT_TYPE, LoadSharedLibrary and GetFunctionAddress), I am developing on Linux (Ubuntu 9.10). Ideally, I would like the library loading implementation to be cross platform (since I am using ANSI C code). But if I have to choose one platform, it will have to be the Linux platform.

I would be very grateful if anyone could shed some light on how I can invoke functions in arbitrary shared libraries (ideally, in a cross platform way - failing that, on Linux), so that I can implement the above function.

Dynamic shared library loading framework

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在使用一个遗留的C库，它可以通过编写用户定义的函数，然后重新编译源代码来扩展。我想避免编译需求，而是使用函数扩展一次(参见下面的伪代码)：此函数将按如下方式实现：VARIANT_TYPE CallSharedLibFunction(const char* library_name, const char* func...

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