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我决定是时候完成我一周前开始的小中缀计算器了，但在我的评估函数中遇到了问题。我的 switch 语句似乎与我通过运算符结构处理数组的方式存在问题。我不完全确定我做错了什么。这不是我遇到的唯一错误，但我确信如果我解决了这个问题，那么其他问题应该更容易解决。显然我的代码不完整，但考虑到我到目前为止所拥有的东西，我是否走在正确的轨道上？

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

bool die(const string &msg);

//stack class
class Stack{
public:
    Stack();
    void push(const double &val);
    void push(const string &oper);
    double popnum();
    string popop();
    double getopele();
    double getnumele();
    unsigned getarity(string token);
    unsigned getprec(string token);
    string topop();
private:
    static const unsigned MAX=30;
    string opstack[MAX];
    double numstack[MAX];
    unsigned opele;
    unsigned numele;
};
//operators
bool add(double &r, double &x, double &y);
bool subtract(double &r, double &x, double &y);
bool multiply(double &r, double &x, double &y);
bool divide(double &r, double &x, double &y);

//operator type
struct OP{
    string name;
    void * func;
    unsigned arity;
    unsigned prec;
    bool lass;
    string descrip;
};
//operator table
OP op[]={{"+", add, 2, 4, true, "2+3 is 5"},
        {"-", subtract, 2, 4, true, "2-3 is -1"},
        {"*", multiply, 2, 6, true, "2*3 is 6"},
        {"/", divide, 2, 6, true, "2/3 is 0.666666..., div by 0 illegal"}};
unsigned OPELE =sizeof(op)/sizeof(op[0]);


//Manip
unsigned findindex(string token);
bool parseval(double &t, const string &token);
double parseforeval(double &result, string line);
void evaluate(double &result, Stack &s);
bool weird(double x);

int main(){
    for(string line; getline(cin, line);){
        if(line=="QUIT") break;
        if(line.empty()) continue;
        if(line=="DOC")
            for(unsigned i=0; i<OPELE; i++)
                cout<<op[i].name<<" | "<<op[i].descrip<<'\n';
        double result;
        if(parseforeval(result, line)){
            cout<<result<<'\n';
        }else{
            cout<<"Could not understand input\n\n";
        }
    }
}

Stack::Stack(){
    opele=0;
    numele=0;
}

void Stack::push(const double &val){
    if(MAX) die("Stack Overflow");
    numstack[numele++]=val;
}

void Stack::push(const string &oper){
    if(MAX) die("Stack Overflow");
    opstack[opele++]=oper;
}

double Stack::popnum(){
    if(!numele) die("Stack Underflow");
    return numstack[--numele];
}

string Stack::popop(){
    if(!opele) die("Stack Underflow");
    return opstack[--opele];
}

double Stack::getopele(){
    return opele;
}

double Stack::getnumele(){
    return numele;
}

unsigned Stack::getprec(string token){
    unsigned i=findindex(token);
    return op[i].prec;
}

unsigned Stack::getarity(string token){
    unsigned i=findindex(token);
    return op[i].arity;
}

string Stack::topop(){
    if(!opele) die("Undeflow");
    return opstack[opele-1];
}

double parsforeval(double &result, string line){
    istringstream sin(line);
    Stack s;
    for(string token; sin>>token;){
        double t;
        if(parseval(t, token)){
            s.push(t);
        }else if(token=="("){
            s.push(parsforeval(result, line));
        }else if(s.getprec(s.topop()) >s.getprec(token)){
            //write eval function
            s.push(token);
        }else if(token== ")"){
            if(!s.getnumele()) die("Bad format");
            return s.popnum();
        }else{
            s.push(token);
        }
    }
    while(s.getopele()){
        evaluate(result, s);
    }
}

void evaluate(double &result, Stack &s){
    unsigned i= findindex(s.popop());
    switch(op[i].arity){
        case 1:
            if(s.getnumele()<1) die("Underflow");
            double x = s.popnum();
            if(  !reinterpret_cast<bool (*)(double &, double &)> !op[i].func (result, x)  ) die("No OP");
            break;
        case 2:
            if(s.getnumele()<2) die("Underflow");
            double y = s.popnum();
            double x = s.popnum();
            if(  !reinterpret_cast<bool (*)(double &, double &,double &)> op[i].func (result, x, y)  ) die("No OP");
            break;
        case 3:
            if(s.getnumele()<3) die("Underflow");
            double z = s.popnum();
            double y = s.popnum();
            double x = s.popnum();
            if(   !reinterpret_cast<bool (*)(double &, double & , double & , double &)>op[i].func (result, x, y, z)   ) die("No OP");
            break;
        default:
            die("uuuuuuhhhh i have no idea");
            break;
    }
    s.push(result);
}

bool add(double &r, double &x, double &y){
    double t = x + y;
    if( weird(t) )  return false;
    r = t;
    return true;
}

bool subtract(double &r, double &x, double &y){
    double t = x - y;
    if( weird(t) )  return false;
    r = t;
    return true;
}

bool multiply( double & r, double& x, double &y ){
    double t = x * y;
    if( weird(t) )  return false;
    r = t;
    return true;
}

bool divide( double & result, double &x, double &y ){
    double t = x / y;
    if( weird(t) )  return false;
    result = t;
    return true;
}

unsigned findindex(string token){
    for(unsigned i=0; i<OPELE; i++)
        if(op[i].name==token)
            return i;
    return UINT_MAX;

}

bool parseval(double &val, const string &token){
    istringstream sin( token );
    double t;
    if( !(sin >>t) )  return false;
    char junk;
    if( sin >>junk )  return false;
    val = t;
    return true;
}

bool weird( double x ){
    return  x != x || x != 0 && x == 2*x;
}

bool die(const string &msg){
    cout<<"Error: "<<msg;
    exit(EXIT_FAILURE);
}
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1 回答 1

1

reinterpret_cast 的参数应该有括号。我认为它可能会将其解析为试图重新解释调用 func 而不是 func 成员本身的结果。

例如

if(  !reinterpret_cast<bool (*)(double &, double &)>(op[i].func) (result, x)  ) die("No OP");
于 2012-12-25T01:52:22.490 回答