<<C++ 沉思錄>> 中文人民郵電出版 勘誤

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<<C++ 沉思錄>> 中文人民郵電出版 勘誤

這本中文版裡面有各種坑爹的小錯誤. 比方說變數名的大小寫, 同一個變數, 出現了大小寫不一致, 等等問題都有.

然後今天感覺遇到了個文法問題. 關於繼承許可權的問題.

書中第八章的demo裡面, 關於class Expr_node.

使用了protected關鍵字. 但是這裡Expr_node是基類, 繼承就會出現問題.

具體的代碼如下:

class Expr_node{    friend ostream& operator << (ostream&, const Expr_node&);    friend class Expr;    int use;// @use is a counter to avoid copying objects.    //protected:    public:        Expr_node(): use(1) { }        virtual void print(ostream&) const = 0;        virtual ~Expr_node() { }        virtual int eval() const = 0;};

這裡用protected就會error.

protected本來就是為了明確不發生繼承的地區. 這裡這堆虛函數是要發生繼承的.就是為了占坑了讓子類去實現.

這裡應該使用public, 而不是 protected.

由於可能在"挑戰權威" , 所以把問題拋出來, 希望有心人能一起討論.

下面是完整的代碼. 可供測試

/*    Programmer  :   EOF    Date        :   2015.05.19    File        :   8.4.cpp    E-mail      :   [email protected] */#include <iostream>#include <string>using namespace std;/*   This @Expr_node is the base-class. */class Expr_node{    friend ostream& operator << (ostream&, const Expr_node&);    friend class Expr;    int use;// @use is a counter to avoid copying objects.    protected:    //public:        Expr_node(): use(1) { }        virtual void print(ostream&) const = 0;        virtual ~Expr_node() { }        virtual int eval() const = 0;};class Expr{    friend ostream& operator<<(ostream&, const Expr&);    Expr_node* p;    public:        Expr():p(NULL){}        Expr(int);        Expr(const string&, Expr);        Expr(const string&, Expr, Expr);        Expr(const Expr& t) { p = t.p; ++p->use; };        Expr& operator=(const Expr&);        ~Expr() { if(--p->use == 0) delete p;}        int eval() const {return p->eval();}};ostream&operator<<(ostream& o, const Expr_node& e){    e.print(o);    return o;}Expr&Expr::operator=(const Expr& rhs){    rhs.p->use++;    if(--p->use == 0)    {        delete p;    }    p = rhs.p;    return *this;}ostream&operator<<(ostream& o, const Expr& t){    t.p->print(o);    return o;}class Int_node: public Expr_node{    friend class Expr;    int n;    Int_node(int k): n(k) { }    void print(ostream& o) const { o << n;}    int eval() const { return n;}};class Unary_node: public Expr_node{    friend class Expr;    string op;    Expr opnd;    Unary_node(const string& a, Expr b):        op(a), opnd(b) { }    void print(ostream& o) const    {        o << "(" << op << opnd << ")";    }    int eval() const    {        if(op == "-")        {            return -opnd.eval();        }        throw "error, bad op" + op + "int UnaryNode";    }};class Binary_node: public Expr_node{    friend class Expr;    string op;    Expr left;    Expr right;    Binary_node(const string& a, Expr b, Expr c):        op(a), left(b), right(c) { }    void print(ostream& o) const    {        o << "(" << left << op << right << ")";    }    int eval() const    {        int op1 = left.eval();        int op2 = right.eval();        if(op == "-") return op1 - op2;        if(op == "+") return op1 + op2;        if(op == "*") return op1 * op2;        if(op == "/") return op1 / op2;        if(op == "/" && op2 != 0) return op1/ op2;        throw "error, bad op" + op + "int BinaryNode";    }};Expr::Expr(int n){    p = new Int_node(n);}Expr::Expr(const string& op, Expr t){    p = new Unary_node(op, t);}Expr::Expr(const string& op, Expr left, Expr right){    p = new Binary_node(op, left, right);}int main(){    Expr t = Expr("*", Expr("-", 5), Expr("+", 3, 4));    cout << t << " = " << t.eval() << endl;    t = Expr("*", t, t);    cout << t << " = " << t.eval() << endl;    return 0;}

<<C++ 沉思錄>> 中文人民郵電出版 勘誤