c++ - 如何在类初始值设定项中声明指向成员函数的指针并通过这些指针进行调用？

Question

我想在我的类中构建一个表，其中包含指向成员函数的指针。 MS C++ (Visual Studio 2015) 编译器提示类中 _requests 表的初始值设定项以及 std::bind 的使用。编译器的错误消息不是很有用:

1>d:\temp\win32project1\win32project1\source1.cpp(59): error C3867: 'tlv::parse_read': non-standard syntax; use '&' to create a pointer to member

1>d:\temp\win32project1\win32project1\source1.cpp(62): error C3867: 'tlv::parse_write': non-standard syntax; use '&' to create a pointer to member

1>d:\temp\win32project1\win32project1\source1.cpp(40): error C2440: 'initializing': cannot convert from 'std::_Binder &>' to 'std::function'

1> d:\temp\win32project1\win32project1\source1.cpp(40): note: No constructor could take the source type, or constructor overload resolution was ambiguous

在表中的例程名称前面放置一个符号只是将错误更改为对绑定(bind)成员函数的非法操作

#include <cstdint>
#include <functional>
#include <vector>
#include <iostream>

using namespace std;

enum TLV_TYPE : uint32_t
    {
    tlv_type_read,
    tlv_type_write
    };

typedef struct
    {
    TLV_TYPE    type;
    uint32_t     length;
    } TLV_RECORD, *pTLV_RECORD;

typedef function <uint32_t (const TLV_RECORD& Record)> pTLV_PARSER;

typedef struct
    {
    TLV_TYPE            type;
    pTLV_PARSER         parse_routine;
    } TABLE, *pTABLE;

class tlv
    {
    public:
        tlv ()
            {
            };
        ~tlv ()
            {
            };

        uint32_t start_parse (const TLV_RECORD& Record)
            {
            pTLV_PARSER parser = std::bind (_requests [0].parse_routine, this, placeholders::_1);
            parser (Record);
            return 0;
            };

    protected:

        uint32_t parse_read (const TLV_RECORD& Record)
            {
            cout << "parse read: type " << Record.type << endl;
            return 0;
            }

        uint32_t parse_write (const TLV_RECORD& Record)
            {
            cout << "parse write: type " << Record.type << endl;
            return 0;
            }

        const TABLE _requests [2] =
            {
                {tlv_type_read, parse_read},
                {tlv_type_write, parse_write},
            };

    };  // End of class tlv

int main ()
    {
    tlv         foo;
    TLV_RECORD  rec = {tlv_type_read, 4};

    foo.start_parse (rec);
    return 0;
    }

Answer 1

一种方法是在 tlv 的构造函数初始化列表中初始化 _requests，这样就会有一个可以绑定(bind)的 this 指针。我还建议使用 lambda 函数而不是 std::bind，因为它们通常更快。

tlv () :
    _requests{
        {tlv_type_read,  [this](const TLV_RECORD& Record){ return parse_read(Record); }},
        {tlv_type_write, [this](const TLV_RECORD& Record){ return parse_write(Record); }}
    }
{
}

uint32_t start_parse (const TLV_RECORD& Record)
{
    pTLV_PARSER parser = _requests[0].parse_routine;
    parser (Record);
    return 0;
};

const TABLE _requests [2];