指向C ++类成员函数作为全局函数参数的指针？ [英] Pointer to a C++ class member function as a global function's parameter?

问题描述

我在调用全局函数时遇到了问题，该函数将指向函数的指针作为参数。
这是全局函数的声明：

int lmdif ( minpack_func_mn fcn, void *p, int m, int n, double *x, 
            double *fvec, double ftol)

minpack_func_mn符号是用于指向函数的指针的typedef，定义为：

The "minpack_func_mn" symbol is a typedef for a pointer to a function, defined as:

typedef int (*minpack_func_mn)(void *p, int m, int n, const double *x, 
              double *fvec, int iflag );

我想使用指向a成员函数的指针来调用 lmdif函数我创建的类，这是该类函数的声明：

I want to call the "lmdif" function with a pointer to a function which is a member of a class I created, and here is the declaration of this class function:

int LT_Calibrator::fcn(void *p, int m, int n, const double *x, 
                       double *fvec,int iflag)

I正在调用这样的全局函数：

I am calling a global function like this:

info=lmdif(&LT_Calibrator::fcn, 0, m, n, x, fvec, ftol)

不幸的是，我得到了一个编译器错误，它表示：
错误C2664：'lmdif'：无法将参数1从'int（__thiscall LT_Calibrator :: *）（void *，int，int，const double *，double *，int）'转换为'minpack_func_mn'
1>那里没有可以进行这种转换的上下文。

Unfortunately, I get a compiler error, which says: "error C2664: 'lmdif' : cannot convert parameter 1 from 'int (__thiscall LT_Calibrator::* )(void *,int,int,const double *,double *,int)' to 'minpack_func_mn' 1> There is no context in which this conversion is possible"

有没有办法解决这个问题？

Is there any way to solve that problem?

推荐答案

您需要一个非成员或静态成员函数；成员函数指针不能代替您的函数类型，因为它需要实例来调用它。

You need a non-member or static member function; a member function pointer can't be used in place of your function type because it requires an instance to call it on.

如果您的函数不需要访问a LT_Calibrator 实例，则可以简单地将其声明为静态，或使其具有自由功能。否则，您似乎可以使用第一个参数（ void * p ）将实例指针传递到蹦床函数中，然后可以调用成员函数。与此类似：

If your function doesn't need access to a LT_Calibrator instance, then you can simply declare it static, or make it free function. Otherwise, it looks like you can use the first argument (void *p) to pass an instance pointer into a "trampoline" function, which can then call a member function. Something along the lines of this:

// member function
int LT_Calibrator::fcn(int m, ...);

// static (or non-member) trampoline
static int fcn_trampoline(void *p, int m, ...)
{
    return static_cast<LT_Calibrator*>(p)->fcn(m,...);
}

info = lmdif(&fcn_trampoline, this, m, ...);

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