C++ 中的异常处理
- catch 语句块中可以抛出异常
编程实验: catch 中抛出异常
#include <iostream>
using namespace std;
int main()
{
try
{
try
{
throw 'c';
}
catch(int i)
{
cout << "Inner: catch(int i)" << endl;
throw i;
}
catch(...)
{
cout << "Inner: catch(...)" << endl;
throw;
}
}
catch(...)
{
cout << "Outer: catch(...)" << endl;
}
return 0;
}
输出:
Inner: catch(...)
Outer: catch(...)
问题:
为什么要在 catch 中重新抛出异常?
- catch 中捕获得异常可以被重新解释后抛出
- 工程开发中使用这样得方式统一异常类型
编程实验: 异常的重新解释
#include <iostream>
using namespace std;
/*
假设: 当前的函数是第三方库中的函数,因此,我们无法修改源代码
函数名: void func(int i)
抛出异常的类型: int
-1 ==》 参数异常
-2 ==》 运行异常
-3 ==》 超时异常
*/
void func(int i)
{
if( i < 0 )
{
throw -1;
}
if( i > 100 )
{
throw -2;
}
if( i == 11 )
{
throw -3;
}
cout << "Run func... " << endl;
}
void MyFunc(int i)
{
try
{
func(i);
}
catch(int i)
{
switch(i)
{
case -1:
throw "Invalid Parameter";
break;
case -2:
throw "Runtime Exception";
break;
case -3:
throw "Timeout Exception";
break;
}
}
}
int main()
{
try
{
MyFunc(11);
}
catch(const char* cs)
{
cout << "Exception Info: " << cs << endl;
}
return 0;
}
输出:
Exception Info: Timeout Exception
- 异常的类型可以是自定义类型
- 对于类类型异常的匹配依旧是至上而下严格匹配
赋值兼容性原则
在异常匹配中依然适用一般而言
- 匹配子类异常的 catch 放在上部
- 匹配父类异常的 catch 放在下部
- 工程中会定义一系列的异常类
- 每个类代表工程中可能出现的一种异常类型
- 代码复用时可能需要重解释不同的异常类
- 在定义 catch 语句块时推荐使用引用作为参数(避开拷贝构造,提高程序效率)
编程实验: 类类型的异常
#include <iostream>
#include <string>
using namespace std;
class Base
{
};
class Exception : public Base
{
private:
int m_id;
string m_desc;
public:
Exception(int id, string desc)
{
m_id = id;
m_desc = desc;
}
int id() const
{
return m_id;
}
string description() const
{
return m_desc;
}
};
/*
假设: 当前的函数是第三方库中的函数,因此,我们无法修改源代码
函数名: void func(int i)
抛出异常的类型: int
-1 ==》 参数异常
-2 ==》 运行一场
-3 ==》 超时异常
*/
void func(int i)
{
if( i < 0 )
{
throw -1;
}
if( i > 100 )
{
throw -2;
}
if( i == 11 )
{
throw -3;
}
cout << "Run func... " << endl;
}
void MyFunc(int i)
{
try
{
func(i);
}
catch(int i)
{
switch(i)
{
case -1:
throw Exception(-1, "Invalid Parameter");
break;
case -2:
throw Exception(-2, "Runtime Exception");
break;
case -3:
throw Exception(-3, "Timeout Exception");
break;
}
}
}
int main()
{
try
{
MyFunc(11);
}
catch(const Exception& e)
{
cout << "Exception Info: " << endl;
cout << " ID: " << e.id() << endl;
cout << " Description: " << e.description() << endl;
}
return 0;
}
输出:
Exception Info:
ID: -3
Description: Timeout Exception
- C++ 标准库中提供了实用异常类
- 标准库中的异常都是从 exception 类派生的
exception 类主要有两个主要的分支
logic_error
- 常用于程序中的可避免逻辑错误
runtime_error
- 常用于程序中无法避免的恶性错误
- 标准库中的异常
编程实验: 标准库中的异常使用
Array.h
#ifndef _ARRAY_H_
#define _ARRAY_H_
#include <stdexcept>
using namespace std;
template
< typename T, int N >
class Array
{
private:
T m_array[N];
public:
int length() const;
bool set(int index, T value);
bool get(int index, T& value);
T& operator[] (int index);
T operator[] (int index) const;
virtual ~Array();
};
template
< typename T, int N >
int Array<T, N>::length() const
{
return N;
}
template
< typename T, int N >
bool Array<T, N>::set(int index, T value)
{
bool ret = (index >=0) && (index < N);
if( ret )
{
m_array[index] = value;
}
return ret;
}
template
< typename T, int N >
bool Array<T, N>::get(int index, T& value)
{
bool ret = (index >=0) && (index < N);
if( ret )
{
value = m_array[index];
}
return ret;
}
template
< typename T, int N >
T& Array<T, N>::operator[] (int index)
{
if( (index >=0) && (index < N) )
{
return m_array[index];
}
else
{
throw out_of_range("T& Array<T, N>::operator[] (int index)");
}
}
template
< typename T, int N >
T Array<T, N>::operator[] (int index) const
{
if( (index >=0) && (index < N) )
{
return m_array[index];
}
else
{
throw out_of_range("T Array<T, N>::operator[] (int index)");
}
}
template
< typename T, int N >
Array<T, N>::~Array()
{
}
#endif
HeapArray.h
#ifndef _HEAPRRAY_H_
#define _HEAPARRAY_H_
#include <stdexcept>
using namespace std;
template
< typename T >
class HeapArray
{
private:
int m_length;
T* m_pointer;
HeapArray(int len);
HeapArray(const HeapArray& obj);
bool construct();
public:
static HeapArray* NewInstance(int length);
int length() const;
bool get(int index, T& value);
bool set(int index, T value);
T& operator [] (int index);
T operator [] (int index) const;
HeapArray& operator = (const HeapArray& obj);
HeapArray& self();
const HeapArray& self() const;
~HeapArray();
};
template
< typename T >
HeapArray<T>::HeapArray(int len)
{
m_length = len;
}
template
< typename T >
bool HeapArray<T>::construct()
{
m_pointer = new T[m_length];
return m_pointer != NULL;
}
template
< typename T >
HeapArray<T>* HeapArray<T>::NewInstance(int length)
{
HeapArray<T>* ret = new HeapArray(length);
if( !(ret && (ret->construct())) )
{
delete ret;
ret = 0;
}
return ret;
}
template
< typename T >
int HeapArray<T>::length() const
{
return m_length;
}
template
< typename T >
bool HeapArray<T>::get(int index, T& value)
{
bool ret = (index >= 0) && (index < length());
if( ret )
{
value = m_pointer[index];
}
return ret;
}
template
< typename T >
bool HeapArray<T>::set(int index, T value)
{
bool ret = (index >= 0) && (index < length());
if( ret )
{
m_pointer[index] = value;
}
return ret;
}
template
< typename T >
T& HeapArray<T>:: operator [] (int index)
{
if( (index >= 0) && (index < length()) )
{
return m_pointer[index];
}
else
{
throw out_of_range("T& HeapArray<T>::operator[] (int index)");
}
}
template
< typename T >
T HeapArray<T>:: operator [] (int index) const
{
if( (index >= 0) && (index < length()) )
{
return m_pointer[index];
}
else
{
throw out_of_range("T HeapArray<T>::operator[] (int index)");
}
}
template
< typename T >
HeapArray<T>& HeapArray<T>:: operator = (const HeapArray<T>& obj)
{
if( this != &obj )
{
T* pointer = new T[obj.m_length];
if( pointer )
{
for(int i=0; i<obj.m_length; i++)
{
pointer[i] = obj.m_pointer[i];
}
m_length = obj.m_length;
delete m_pointer;
m_pointer = pointer;
}
}
return *this;
}
template
< typename T >
HeapArray<T>& HeapArray<T>::self()
{
return *this;
}
template
< typename T >
const HeapArray<T>& HeapArray<T>::self() const
{
return *this;
}
template
< typename T >
HeapArray<T>::~HeapArray()
{
delete[] m_pointer;
}
#endif
main.cpp
#include <iostream>
#include "Array.h"
#include "HeapArray.h"
using namespace std;
void TestArray()
{
Array<int, 5> a;
for(int i=0; i<a.length(); i++)
{
a[i] = i;
}
for(int i=0; i<a.length(); i++)
{
cout << a[i] << endl;
}
}
void TestHeapArray()
{
HeapArray<double>* pa = HeapArray<double>::NewInstance(5);
if( pa != NULL )
{
HeapArray<double>& array = pa->self();
for(int i=0; i<array.length(); i++)
{
array[i] = i;
}
for(int i=0; i<array.length(); i++)
{
cout << array[i] << endl;
}
}
delete pa;
}
int main()
{
try
{
TestArray();
cout << endl;
TestHeapArray();
}
catch(...)
{
cout << "Exception" << endl;
}
return 0;
}
输出:
0
1
2
3
4
0
1
2
3
4
小结
- catch 语句块中可以抛出异常
- 异常的类型可以是自定义类类型
- 赋值兼容性在异常匹配中依然适用
- 标准库中的异常都是从 exception 类派生的
以上内容参考狄泰软件学院系列课程,请大家保护原创
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