= 异常 =
== 错误处理 ==
如果出现本身不能处理的错误，那么发生错误的代码和处理错误的代码不在同一处。常用的错误处理的方式
 * 终止程序
 * 返回一个表示错误的值
 * 默默的返回
 * 设置全局出错变量
 * 抛出异常
{{{#!cplusplus
class Stack {
    int size;
    int capacity;
public:
    void push(int x) {
        if(size >= capacity) {
            // 出错怎么办？
        }
    }
    int pop() {
        if(size <= 0) {
            // 出错怎么办？
        }
    }
};

int main() {
    Stack s;
    s.pop();    // 万一出错怎么办
    s.push(10); // 万一出错怎么办？
}
}}}

== 异常处理方式 ==
{{{#!cplusplus
class Overflow {
};

class Stack {
    int size;
    int capacity;
public:
    void push(int x) {
        if(size >= capacity) {
            Overflow e;
            throw e;
        }       
    }
};

int main() {
    Stack s;
    try {
        s.push(10);
    }
    catch(Overflow e) {
        cout << "Overflow" << endl;
    }
}
}}}

== 处理多种异常 ==
{{{#!cplusplus
class Overflow {
};

class Underflow{
};

class Stack {
    int size;
    int capacity;
public:
    void push(int x) {
        if(size >= capacity) {
            Overflow e;
            throw e;
        }       
    }
    void pop() {
        if(size <=0)
            throw Underflow();
    }
};

int main() {
    Stack s;
    try {
        s.pop();
        s.push(10);
    }
    catch(Overflow e) {
        cout << "Overflow" << endl;
    }
    catch(Underflow e) {
        cout << "Underflow" << endl;
    }
}
}}}


给异常添加派生结构：
{{{#!cplusplus
class StackError {
};

class Overflow : public StackError {
};

class Underflow : public StackError{
};

class Stack {
    int size;
    int capacity;
public:
    void push(int x) {
        if(size >= capacity) {
            Overflow e;
            throw e;
        }       
    }
    void pop() {
        if(size <=0)
            throw Underflow();
    }
};

int main() {
    Stack s;
    try {
        s.pop();
        s.push(10);
    }
    catch(Overflow e) {
        cout << "Overflow" << endl;
    }
    catch(Underflow e) {
        cout << "Underflow" << endl;
    }
    catch(StackError e) {
        cout << "StackError" << endl;
    }
}
}}}

捕捉所有未知异常
{{{#!cplusplus
class StackError {
};

class Overflow : public StackError {
};

class Underflow : public StackError{
};

class Stack {
    int size;
    int capacity;
public:
    void push(int x) {
        if(size >= capacity) {
            throw "Error";
        }
    }
    void pop() {
        if(size <=0)
            throw Underflow();
    }
};

int main() {
    Stack s;
    try {
        s.pop();
        s.push(10);
    }
    catch(Overflow e) {
        cout << "Overflow" << endl;
    }
    catch(Underflow e) {
        cout << "Underflow" << endl;
    }
    catch(StackError e) {
        cout << "StackError" << endl;
    }
    catch(...) {
        cout << "Unknown Error" << endl;
    }
}
}}}

== 标准异常体系 ==

在头文件<exception>中定义了基类exception。

dynamic_cast转换引用出错：bad_cast

new分配内存出错：bad_alloc

at访问成员：out_of_range

{{attachment:diagram16.png}}

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CategoryCpp