初级菜鸟问一个弱智的类内函数指针数组定义问题，求指点

2017-08-07 05:03:37 472 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

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class Widget

{

    Widget()

    {

        pa[0] = &f;

        pa[1] = &g;

        pa[2] = &i;

        pa[3] = &j;

    }



    void select(int idx)

    {

        (this->*pa[idx])();

    }



private:

    void f(){cout<<"void f()"<<endl;}

    void g(){cout<<"void g()"<<endl;}

    void i(){cout<<"void i()"<<endl;}

    void j(){cout<<"void j()"<<endl;}

    enum {cnt = 4};

    void (Widget::*pa[cnt])() ={f,g,i,j};

};

void (Widget::*pa[cnt])() ={f,g,i,j}; //这一行一直报错，Widget::Widget::pa”: 无法指定数组的显式初始值设定项，编译器用的QT

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做或不做 2017-08-11

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以下观点仅是个人对于问题解决方法的倾向并不是想误导别人。仅供参考。首先纠正下你一个问题编译器用的qt这句话总感觉怪怪的。不知道上面的人为什么没有纠正。不讨论问题本质。如果你使用的是VS2015的编译器的话我猜测大概率你是可以编译过去的。如果你是在widows下编程那么你编译器用的只能是 VS2010 VS2012 VS2013 VS2015等其中的一个吧。 msvc是编译器，QT只是一个界面框架。特别的就是实现中采用了有别于C++模板的元对象编程技术。给你讲一个故事就是说美国人为了在太空设计一种可以使用的墨水钢笔花费了100万研究出来苏联人不使用这种带墨水的钢笔直接使用电子笔。其实我想说的是就算是C++11的标准也可以通过非C++11标准的C++重写成别的样子。不要纠结怎么可以编译过去。假设就算打死你都不可能编译的过去你就算怎么改感觉也是无济于事的。因为前面根本就没有路。

Really_want 2017-08-10

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#include <iostream>

using namespace std;

//g++ -g -Wall -std=c++11 -o a.exe main.cpp

struct A
{
	int a[2] = {1,2}; //C++11支持这种语法
};

int main(int argc,char* agrv[])
{
	A a;
	cout<< a.a[0] << "," << a.a[1] <<endl;
	return 0;
}

caozhiyi1 2017-08-08

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成员变量能直接初始化吗？

jena_wy 2017-08-08

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只有静态常量整型数据成员才可以在类中初始化

呵呵程序喵 2017-08-07

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您说的我还不太明白，我改用了public试了，依然不行，这跟C++11关系大吗？我用的是比较新的QT版本

引用 9 楼 ccssddnn218 的回复:

好吧，其实跟是否private没关系，重点是c++11 我排错时，在还没有用C++11前有private的提示，误以为有区别了。

呵呵程序喵 2017-08-07

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多谢！我再自己分析一下

引用 6 楼 zhao4zhong1 的回复:

仅供参考：

#include <stdio.h>
double A[300][100];
double valuex[300];
double valuey[300];
int i;
double fun00(double x,double y) {return x  +   y  ;};
double fun01(double x,double y) {return x*x+ 3*y  ;};
double fun02(double x,double y) {return x  + 2*y*x;};
//...  fun03(double x,double y) {return ...+...   ;};
//...
//...  fun98(double x,double y) {return ...+...   ;};
double fun99(double x,double y) {return x/2+20*y  ;};
double (*funNN[100])(double,double)={
    fun00,
    fun01,
    fun02,
//  fun03,
//  ...
//  fun98,
    fun99,
};
int main() {
    double x,y;
    int f,FN;

    for (i=0;i<300;i++) {
        valuex[i]=(double)i;
        valuey[i]=(double)i;
    }
    FN=3;
    for (i=0;i<300;i++) {
         x=valuex[i];
         y=valuey[i];
         for (f=0;f<FN;f++) A[i][f]=funNN[f](x,y);
    }
    for (i=0;i<3;i++) {
        for (f=0;f<FN;f++) printf("%lg ",A[i][f]);
        printf("\n");
    }
	return 0;
}
//0 0 0
//2 4 3
//4 10 10

Really_want 2017-08-07

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好吧，其实跟是否private没关系，重点是c++11 我排错时，在还没有用C++11前有private的提示，误以为有区别了。

Really_want 2017-08-07

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引用 3 楼 m0_38024304 的回复:

多谢大家回复！ @赵4老师加static依然不行 @ccssddnn218 我改用了private 依然不行，完整程序如下，用的QT，我看的王桂林老师的视频，他在讲课时这样做就行

#include <iostream>

using namespace std;

class Widget
{
public:
    Widget()
    {
        pa[0] = &f;
        pa[1] = &g;
        pa[2] = &i;
        pa[3] = &j;
    }

    void select(int idx)
    {
        (this->*pa[idx])();
    }

private:
    void f(){cout<<"void f()"<<endl;}
    void g(){cout<<"void g()"<<endl;}
    void i(){cout<<"void i()"<<endl;}
    void j(){cout<<"void j()"<<endl;}
    enum {cnt = 4};
    void (Widget::*pa[cnt])() ={f,g,i,j};
};

int main()
{
    Widget w;
    w.select(2);
    return 0;
}

1. 我说了用private不行！！！我代码中使用的是public。 2. 你可能没注意我图片中的标识，需要C++11标准支持

赵4老师 2017-08-07

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再供参考：

//C++ Operators
//  Operators specify an evaluation to be performed on one of the following:
//    One operand (unary operator)
//    Two operands (binary operator)
//    Three operands (ternary operator)
//  The C++ language includes all C operators and adds several new operators.
//  Table 1.1 lists the operators available in Microsoft C++.
//  Operators follow a strict precedence which defines the evaluation order of
//expressions containing these operators.  Operators associate with either the
//expression on their left or the expression on their right;    this is called
//“associativity.” Operators in the same group have equal precedence and are
//evaluated left to right in an expression unless explicitly forced by a pair of
//parentheses, ( ).
//  Table 1.1 shows the precedence and associativity of C++ operators
//  (from highest to lowest precedence).
//
//Table 1.1   C++ Operator Precedence and Associativity
// The highest precedence level is at the top of the table.
//+------------------+-----------------------------------------+---------------+
//| Operator         | Name or Meaning                         | Associativity |
//+------------------+-----------------------------------------+---------------+
//| ::               | Scope resolution                        | None          |
//| ::               | Global                                  | None          |
//| [ ]              | Array subscript                         | Left to right |
//| ( )              | Function call                           | Left to right |
//| ( )              | Conversion                              | None          |
//| .                | Member selection (object)               | Left to right |
//| ->               | Member selection (pointer)              | Left to right |
//| ++               | Postfix increment                       | None          |
//| --               | Postfix decrement                       | None          |
//| new              | Allocate object                         | None          |
//| delete           | Deallocate object                       | None          |
//| delete[ ]        | Deallocate object                       | None          |
//| ++               | Prefix increment                        | None          |
//| --               | Prefix decrement                        | None          |
//| *                | Dereference                             | None          |
//| &                | Address-of                              | None          |
//| +                | Unary plus                              | None          |
//| -                | Arithmetic negation (unary)             | None          |
//| !                | Logical NOT                             | None          |
//| ~                | Bitwise complement                      | None          |
//| sizeof           | Size of object                          | None          |
//| sizeof ( )       | Size of type                            | None          |
//| typeid( )        | type name                               | None          |
//| (type)           | Type cast (conversion)                  | Right to left |
//| const_cast       | Type cast (conversion)                  | None          |
//| dynamic_cast     | Type cast (conversion)                  | None          |
//| reinterpret_cast | Type cast (conversion)                  | None          |
//| static_cast      | Type cast (conversion)                  | None          |
//| .*               | Apply pointer to class member (objects) | Left to right |
//| ->*              | Dereference pointer to class member     | Left to right |
//| *                | Multiplication                          | Left to right |
//| /                | Division                                | Left to right |
//| %                | Remainder (modulus)                     | Left to right |
//| +                | Addition                                | Left to right |
//| -                | Subtraction                             | Left to right |
//| <<               | Left shift                              | Left to right |
//| >>               | Right shift                             | Left to right |
//| <                | Less than                               | Left to right |
//| >                | Greater than                            | Left to right |
//| <=               | Less than or equal to                   | Left to right |
//| >=               | Greater than or equal to                | Left to right |
//| ==               | Equality                                | Left to right |
//| !=               | Inequality                              | Left to right |
//| &                | Bitwise AND                             | Left to right |
//| ^                | Bitwise exclusive OR                    | Left to right |
//| |                | Bitwise OR                              | Left to right |
//| &&               | Logical AND                             | Left to right |
//| ||               | Logical OR                              | Left to right |
//| e1?e2:e3         | Conditional                             | Right to left |
//| =                | Assignment                              | Right to left |
//| *=               | Multiplication assignment               | Right to left |
//| /=               | Division assignment                     | Right to left |
//| %=               | Modulus assignment                      | Right to left |
//| +=               | Addition assignment                     | Right to left |
//| -=               | Subtraction assignment                  | Right to left |
//| <<=              | Left-shift assignment                   | Right to left |
//| >>=              | Right-shift assignment                  | Right to left |
//| &=               | Bitwise AND assignment                  | Right to left |
//| |=               | Bitwise inclusive OR assignment         | Right to left |
//| ^=               | Bitwise exclusive OR assignment         | Right to left |
//| ,                | Comma                                   | Left to right |
//+------------------+-----------------------------------------+---------------+

赵4老师 2017-08-07

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仅供参考：

#include <stdio.h>
double A[300][100];
double valuex[300];
double valuey[300];
int i;
double fun00(double x,double y) {return x  +   y  ;};
double fun01(double x,double y) {return x*x+ 3*y  ;};
double fun02(double x,double y) {return x  + 2*y*x;};
//...  fun03(double x,double y) {return ...+...   ;};
//...
//...  fun98(double x,double y) {return ...+...   ;};
double fun99(double x,double y) {return x/2+20*y  ;};
double (*funNN[100])(double,double)={
    fun00,
    fun01,
    fun02,
//  fun03,
//  ...
//  fun98,
    fun99,
};
int main() {
    double x,y;
    int f,FN;

    for (i=0;i<300;i++) {
        valuex[i]=(double)i;
        valuey[i]=(double)i;
    }
    FN=3;
    for (i=0;i<300;i++) {
         x=valuex[i];
         y=valuey[i];
         for (f=0;f<FN;f++) A[i][f]=funNN[f](x,y);
    }
    for (i=0;i<3;i++) {
        for (f=0;f<FN;f++) printf("%lg ",A[i][f]);
        printf("\n");
    }
	return 0;
}
//0 0 0
//2 4 3
//4 10 10

sdghchj 2017-08-07

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void (Widget::*pa[cnt])() ={&f,&g,&i,&j};

赵4老师 2017-08-07

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《深度探索C++对象模型》《C++反汇编与逆向分析技术揭秘》

呵呵程序喵 2017-08-07

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#include <iostream>

using namespace std;

class Widget
{
public:
    Widget()
    {
        pa[0] = &f;
        pa[1] = &g;
        pa[2] = &i;
        pa[3] = &j;
    }

    void select(int idx)
    {
        (this->*pa[idx])();
    }

private:
    void f(){cout<<"void f()"<<endl;}
    void g(){cout<<"void g()"<<endl;}
    void i(){cout<<"void i()"<<endl;}
    void j(){cout<<"void j()"<<endl;}
    enum {cnt = 4};
    void (Widget::*pa[cnt])() ={f,g,i,j};
};

int main()
{
    Widget w;
    w.select(2);
    return 0;
}

Really_want 2017-08-07

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#include <iostream>

using namespace std;

class Widget

{

public: //构造函数要public

    Widget()

    {

        pa[0] = &f;

        pa[1] = &g;

        pa[2] = &i;

        pa[3] = &j;

    }



    void select(int idx)

    {

        (this->*pa[idx])();

    }



public: //private不行

    void f(){cout<<"void f()"<<endl;}

    void g(){cout<<"void g()"<<endl;}

    void i(){cout<<"void i()"<<endl;}

    void j(){cout<<"void j()"<<endl;}

    enum {cnt = 4};

    void (Widget::*pa[cnt])() ={f,g,i,j};

};

int main()

{

	Widget w;

	w.select(2);

	return 0;

}

赵4老师 2017-08-07

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加static ？

初级菜鸟问一个弱智的类内函数指针数组定义问题，求指点

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