怎样在C中调用C++函数

How do I call a C++ function from C?


Just declare the C++ function ``extern "C"'' (in your C++ code) and call it (from your C or C++ code). For example:

	// C++ code:
extern "C" void f(int);
void f(int i)
{
// ...
}

Now f() can be used like this:

	/* C code: */
void f(int);
void cc(int i)
{
f(i);
/* ... */
}

Naturally, this works only for non-member functions. If you want to call member functions (incl. virtual functions) from C, you need to provide a simple wrapper. For example:

	// C++ code:
class C {
// ...
virtual double f(int);
};

extern "C" double call_C_f(C* p, int i) // wrapper function
{
return p->f(i);
}

Now C::f() can be used like this:

	/* C code: */
double call_C_f(struct C* p, int i);
void ccc(struct C* p, int i)
{
double d = call_C_f(p,i);
/* ... */
}

If you want to call overloaded functions from C, you must provide wrappers with distinct names for the C code to use. For example:

	// C++ code:
void f(int);
void f(double);
extern "C" void f_i(int i) { f(i); }
extern "C" void f_d(double d) { f(d); }

Now the f() functions can be used like this:

	/* C code: */
void f_i(int);
void f_d(double);
void cccc(int i,double d)
{
f_i(i);
f_d(d);
/* ... */
}

Note that these techniques can be used to call a C++ library from C code even if you cannot (or do not want to) modify the C++ headers.

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