将变量发送到void指针或C ++中的void指针引用中

Question

我正在尝试map boost::functions 。 因此，我可以使用带有输入和输出参数的字符串名称来调用它们。

例：

 MyFuncs::CallFunc("MyClass::TestFunc", void* input, void* output);

我想创建输入和输出变量，并将它们的指针发送到MyFuncs::CallFunc()进行处理。

我可以将(void* input)指针发送到函数中，并将其值提取为int，string等。

我无法发送分配自己的空间来接收值的(void* output) 。 我必须在调用的函数内部创建一个new type(var) ，否则一旦函数返回，变量将超出范围。

MyFuncs.h

//MyFuncs.h
#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <map>

class MyFuncs
{
public:

    static std::map<std::string, boost::function<void (void*, void*&)> > myfuncs;

    template<class T>
    static void RegisterFunc(const std::string& name, void (T::*func) (void*, void*&), T* instance)
    {
        myfuncs[name] = boost::bind(func, instance, _1, _2);
    }

    static void CallFunc(const std::string& name, void* input, void*& output)
    {
        myfuncs[name](input, output);
    }
};

std::map<std::string, boost::function<void (void*, void*&)> > MyFuncs::myfuncs;

MyClass.h

//MyClass.h 
#include "MyFuncs.h"

class MyClass
{
public:
    MyClass()
    {
        MyFuncs::RegisterFunc("MyClass::GetNumber",  &MyClass::GetNumber,  this);
        MyFuncs::RegisterFunc("MyClass::GetString",  &MyClass::GetString,  this);
        MyFuncs::RegisterFunc("MyClass::EditNumber", &MyClass::EditNumber, this);
        MyFuncs::RegisterFunc("MyClass::EditString", &MyClass::EditString, this);
    }

    void GetNumber(void* input, void*& output)
    {
        int var = 1234;
        output = static_cast<void*>(new int(var));             //WORKS, var eats memory
        //output = static_cast<void*>(&var);                   //ERROR, var goes out of scope
    }

    void GetString(void* input, void*& output)
    {
        std::string var = "Get test";
        output = static_cast<void*>(new std::string(var));     //WORKS, var eats memory
        //output = static_cast<void*>(&var);                   //ERROR, var goes out of scope
    }

    void EditNumber(void* input, void*& output)
    {
        int var = *static_cast<int*>(input);                   //WORKS, var gets 4321 OK
        output = static_cast<void*>(new int(var));             //WORKS, var eats memory
        //output = static_cast<void*>(&var);                   //ERROR, var goes out of scope
    }

    void EditString(void* input, void*& output)
    {
        std::string var = *static_cast<std::string*>(input);   //WORKS, var gets "Edit test" OK
        output = static_cast<void*>(new std::string(var));     //WORKS, var eats memory
        //output = static_cast<void*>(&var);                   //ERROR, var goes out of scope
    }
};

MyApp.cpp

//MyApp.cpp 
#include "MyClass.h"

void main()
{
    MyClass myclass;

    void* in;
    void* out;

    MyFuncs::CallFunc("MyClass::GetNumber", NULL, out);  //atempting to fill the variable
    int getNumOut = *static_cast<int*>(out);
    printf("MyClass::GetNumber = %d \n", getNumOut);

    MyFuncs::CallFunc("MyClass::GetString", NULL, out);  //atempting to fill the variable
    std::string getStrOut = *static_cast<std::string*>(out);
    printf("MyClass::GetString = %s \n", getStrOut.c_str());

    int editNum = 4321;
    in = static_cast<void*>(&editNum);
    MyFuncs::CallFunc("MyClass::EditNumber", in, out);  //atempting to fill the variable
    int editNumOut = *static_cast<int*>(out);
    printf("MyClass::EditNumber = %d \n", editNumOut);

    std::string editStr = "Edit test";
    in = static_cast<void*>(&editStr);
    MyFuncs::CallFunc("MyClass::EditString", in, out);  //atempting to fill the variable
    std::string editStrOut = *static_cast<std::string*>(out);
    printf("MyClass::EditString = %s \n", editStrOut.c_str());

    getchar(); //wait for close
}

Answer 1

void* out在main内部声明。 为了使out有效，它应该指向寿命至少与main事物。 由于您尚未在类MyClass中声明可以通过out返回的int和string类型的数据成员，因此您需要分配内存。

假设您声明了数据成员int var; 在MyClass类中，则GetNumber如下所示：

class MyClass
{
    private:
             int var;

    public:
    MyClass()
    {
        //Register function
        var = 10;  
    }

    void GetNumber(void* input, void*& output)
    {
        //int var = 1234;  //<-- instead of using local "var", now use MyClass::var i.e this->var
        output = static_cast<void*>(&(this->var));
    }
};

Answer 2

解
在不使用static_cast或额外的boost函数的情况下，我能够使用纯C ++。

*(int*)output = var; 和*(std::string*)output = var; 似乎可以解决问题。


MyFuncs.h

#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <map>

class MyFuncs
{
public:

    //A list of function names linked to boost::functions.
    static std::map<std::string, boost::function<void (void*, void*)> > myfuncs;


    //Register a class function by name.       MyFuncs::RegisterFunc("MyClass::Test", &MyClass::Test, instance);
    template<class T>
    static void RegisterFunc(const std::string& name, void (T::*func) (void*, void*), T* instance)
    {
        myfuncs[name] = boost::bind(func, instance, _1, _2);
    }


    //Call functions by name, with input and output.       MyFunct::CallFunc("MyClass::Test", input, output);
    static void CallFunc(const std::string& name, void* input, void* output)
    {
        myfuncs[name](input, output);
    }
};

std::map<std::string, boost::function<void (void*, void*)> > MyFuncs::myfuncs;

MyClass.h

#include "MyFuncs.h"

class MyClass
{
public:
    MyClass()
    {
        MyFuncs::RegisterFunc("MyClass::GetNumber",  &MyClass::GetNumber,  this);
        MyFuncs::RegisterFunc("MyClass::GetString",  &MyClass::GetString,  this);
        MyFuncs::RegisterFunc("MyClass::EditNumber", &MyClass::EditNumber, this);
        MyFuncs::RegisterFunc("MyClass::EditString", &MyClass::EditString, this);
    }

    void GetNumber(void* input, void* output)
    {
        int var = 1234;
        *(int*)output = var;
    }

    void GetString(void* input, void* output)
    {
        std::string var = "Get test";
        *(std::string*)output = var;
    }

    void EditNumber(void* input, void* output)
    {
        int in = *(int*)input; //4321
        int out = in - 4320;   //result is 1;
        *(int*)output = out;
    }

    void EditString(void* input, void* output)
    {
        std::string in = *(std::string*)input; //"Edit Test"
        std::string out = in += " (edited)";   //result is "Edit test (edited)"
        *(std::string*)output = out;
    }
};

MyApp.cpp

#include "MyClass.h"

void main()
{
    MyClass myclass;

    int getNum;
    MyFuncs::CallFunc("MyClass::GetNumber", NULL, &getNum);
    printf("MyClass::GetNumber = %d \n", getNum);

    std::string getStr;
    MyFuncs::CallFunc("MyClass::GetString", NULL, &getStr);
    printf("MyClass::GetString = %s \n", getStr.c_str());

    int editNumIn = 4321;
    int editNumOut;
    MyFuncs::CallFunc("MyClass::EditNumber", &editNumIn, &editNumOut);
    printf("MyClass::EditNumber = %d \n", editNumOut);

    std::string editStrIn = "Edit test";
    std::string editStrOut;
    MyFuncs::CallFunc("MyClass::EditString", &editStrIn, &editStrOut);
    printf("MyClass::EditString = %s \n", editStrOut.c_str());

    getchar(); //wait for close
}