可以在C函数指针中放置哪些C ++函数? [英] What kinds of C++ functions can be placed in a C function pointer?

问题描述

我有一个C库，该库使用函数指针的结构进行回调.回调将从C代码中调用.

I have a C library that uses a struct of function pointers for callbacks. The callbacks will be called from C code.

extern "C" {
typedef struct callbacks_t {
    void (*foo) (const char*);
    int  (*bar) (int);  
} callbacks_t;
}// extern C

我可以安全将哪些类型的C ++函数放在要从C库中调用的那些函数指针中?静态成员函数?完全指定的模板功能?不捕获Lambda?

What kinds of C++ functions can I safely place in those function pointers to be called from the C library? Static member functions? Fully specified template functions? Non-capturing Lambdas?

g ++似乎可以让我使用以上所有内容，但是我对C和C ++函数使用不同的调用约定和语言绑定时的安全性表示怀疑.

g++ seemingly lets me use all of the above, but I question the safety when different calling conventions and language bindings are used for C and C++ functions.

推荐答案

我有一个C库，该库使用函数指针的结构进行回调.回调将从C代码中调用.

I have a C library that uses a struct of function pointers for callbacks. The callbacks will be called from C code.

C库仅能理解C.因此，您只能传递C明确支持和理解的内容.

A C library only understands C. So you can only pass back things that are explicitly supported and understood by C.

由于C ++中没有定义任何函数类型的调用约定，因此您不能显式地传回C ++函数.您只能传回C函数(用extern "C"明确声明的C函数)并保证它们兼容.

Since there is no definition of calling conventions for any function types in C++ you can not explicitly pass back C++ functions. You can only pass back C function (those explicitly declared with extern "C") and guarantee that they are compatible.

就像所有未定义的行为一样，这似乎可以正常工作(例如，回传普通的C ++函数或静态成员).但是，像所有未定义的行为一样，它也可以工作.您只是不能保证它实际上是正确的或可移植的.

Like all undefined behavior this may seem to work (like passing back normal C++ functions or static members). But like all undefined behavior it's allowed to work. You just can't guarantee that it's actually correct or portable.

extern "C" {
    typedef struct callbacks_t {
        void (*foo) (const char*);
        int  (*bar) (int);  
    } callbacks_t;

    // Any functions you define in here.
    // You can set as value to foo and bar.

}// extern C

我可以安全地将哪些C ++函数放置在要从C库中调用的那些函数指针中?

What kinds of C++ functions can I safely place in those function pointers to be called from the C library?

静态成员函数?

不.但这恰好适用于许多平台.这是一个常见的错误，会在某些平台上咬人.

No. But this happens to work on a lot of platforms. This is a common bug and will bite people on some platforms.

完全指定的模板功能?

Fully specified template functions?

不.

没有捕获的Lambda?

Non-capturing Lambdas?

否.

g ++似乎可以让我使用以上所有内容，

g++ seemingly lets me use all of the above,

是的.但是，假设您要传递使用C ++编译器构建的对象(这是合法的).由于C ++代码将使用正确的调用约定.问题是，当您将这些东西传递给C库时(就会想到pthreads).

Yes. But it is assuming that you are passing to objects that are built with the C++ compiler (which would be legal). As C++ code will use the correct calling convention. The problem is when you pass these things to a C library (pthreads springs to mind).

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