如何将C ++回调传递给C库函数？ [英] How do I pass a C++ callback to a C library function?

问题描述

我使用C ++开发我的代码，并想使用MPFIT非线性曲线拟合库，它是在C开发的，但允许在C ++中编译。

I'm developing my code using C++ and want to use MPFIT nonlinear curve fitting library, which is developed in C but allows to compile in C++.

例如，我有一个名为myClass的类，该类有一个函数myClass :: Execute（）

For example I have a class named "myClass", and this class has a function myClass::Execute()

我将mpfit.h包含到myClass.h文件中。尝试从Execute（）调用一个名为mpfit的函数。

I include "mpfit.h" to myClass.h file. And try to call a function called mpfit from Execute().

int status = mpfit(ErrorFunction, num1, num2, xsub_1D, 0, 0, (void *) &variables, &result);

问题是ErrorFunction是myClass的函数。所以编译器给出错误时，我尝试使用这个。我尝试从类对象中携带Erro​​rFunction，但这次我采取以下错误：

The problem is ErrorFunction is a function of myClass. So compiler gives error when I try to use this. I tried to carry the ErrorFunction out of the class object, but this time I take the error given below:

ErrorFunction超出类时出错：

Error when the ErrorFunction is outside of the class:

错误4错误C2664：'mpfit'：无法从int
（__cdecl *）（int，int，double * ，double，double *，void *）'到
'mp_func'

Error 4 error C2664: 'mpfit' : cannot convert parameter 1 from 'int (__cdecl *)(int,int,double *,double,double *,void *)' to 'mp_func'

ErrorFunction在类中时出错：

Error when the ErrorFunction is inside the class:

Error   3   error C3867: 'myClass::ErrorFunction': function call missing argument list; use '&myClass::ErrorFunction' to

错误函数的定义：

int ErrorFunction(int dummy1, int dummy2, double* xsub, double *diff, double **dvec, void *vars)

如何调用此函数并将其解析为mpfit，这是一个C函数？

How can I call this function and parse it into mpfit, which is a C function?

mp_func 定义为：

/* Enforce type of fitting function */
typedef int (*mp_func)(int m, /* Number of functions (elts of fvec) */
               int n, /* Number of variables (elts of x) */
               double *x,      /* I - Parameters */
               double *fvec,   /* O - function values */
               double **dvec,  /* O - function derivatives (optional)*/
               void *private_data); /* I/O - function private data*/

推荐答案

确保您的调用约定匹配。 C库使用C调用约定，或cdecl（__cdecl）。如果你在C ++中使用mp_func typedef，它可能默认为编译器的标准调用约定，或stdcall（__stdcall）。要么创建一个新的typedef，要么将其改为：

Make sure that your calling conventions match. C libraries use the C calling convention, or cdecl (__cdecl). If you're using the mp_func typedef within C++, it could be defaulting to the compiler's standard calling convention, or stdcall (__stdcall). Either make a new typedef or change it to the following:

typedef int __cdecl (*mp_func)(int m, /* Number of functions (elts of fvec) */
               int n, /* Number of variables (elts of x) */
               double *x,      /* I - Parameters */
               double *fvec,   /* O - function values */
               double **dvec,  /* O - function derivatives (optional)*/
               void *private_data); /* I/O - function private data*/

当你声明ErrorFunction时， __cdecl：

And when you declare ErrorFunction, also declare it as __cdecl:

int __cdecl ErrorFunction(int, int, double*, double *, double **, void *);

如果编译器仍然抱怨调用mpfit函数时，可以尝试将函数指针转换为mp_func typedef with cdecl：

If the compiler still complains when calling the mpfit function, you can try casting your function pointer to the mp_func typedef with cdecl:

int status = mpfit((mp_func)ErrorFunction, num1, num2, xsub_1D, 0, 0, (void *) &variables, &result);

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