《C++文章汇总》
上一篇介绍了《016-Lamda表达式、C++14和C++17新特性》,本文介绍异常。
1.错误
◼ 编程过程中的常见错误类型 语法错误
逻辑错误
异常
......
2.异常
◼ 异常是一种在程序运行过程中可能会发生的错误(比如内存不够)
int main(){
cout << 1 << endl;
for (int i = 0; i<99999; i++) {
//这句代码可能会产生异常(抛出异常)
try {
int *p = new int[9999999];
cout << 2 << endl;
/**
...
*/
} catch (...) {
cout << "产生异常了:内存不够用" << endl;
break;
}
}
cout << 3 << endl;
}
◼ 异常没有被处理，会导致程序终止,后面的代码不会执行
被除数为0,系统不会抛异常，直接闪退，程序员手动抛异常
图片.png
int divide(int v1,int v2){
if (v2 == 0) {
throw 999;
}
return v1/v2;;
}
int main(){
try {
int a = 10;
int b = 0;
int c = divide(a, b);
cout << c << endl;
} catch (...) {
cout << "产生异常了" << endl;
}
getchar();
return 0;
}
//输出
产生异常了
抛出字符串异常
int divide(int v1,int v2){
if (v2 == 0) {
//抛出异常
throw "不能除以0";
}
return v1/v2;;
}
int main(){
cout << 1 << endl;
try {
int a = 10;
int b = 0;
int c = divide(a, b);
cout << c << endl;
} catch (const char *exception) {
cout << "产生异常了:" << exception << endl;
}
cout << 2 << endl;
getchar();
return 0;
}
//输出
1
产生异常了:999
2
图片.png
try {
int a = 10;
int b = 0;
int c = divide(a, b);
cout << c << endl;
} catch(int exception){
cout << "产生异常了:int exception" << exception << endl;
}catch (const char *exception) {
cout << "产生异常了:const char *exception" << exception << endl;
}
◼ throw异常后，会在当前函数中查找匹配的catch，找不到就 终止当前函数代码，去上一层函数中查找。如果最终都找不 到匹配的catch，整个程序就会终止
异常没有被处理，程序中止
void func1(){
cout << "func1-begin" << endl;
throw 666;//throw 666
cout << "func1-end" << endl;
};
void func2(){
cout << "func2-begin" << endl;;
func1();//throw 666
cout << "func2-end" << endl;
};
int main(){
cout << "main-begin" << endl;
func2();//throw 666
cout << "main-end" << endl;
getchar();
return 0;
}
//输出
main-begin
func2-begin
func1-begin
libc++abi.dylib: terminating with uncaught exception of type int
图片.png
异常被捕获，程序正常执行
void func1(){
cout << "func1-begin" << endl;
try{
throw 666;
}catch(int exception){
cout << "产生异常了:(int)" << exception << endl;
}
cout << "func1-end" << endl;
};
void func2(){
cout << "func2-begin" << endl;;
func1();
cout << "func2-end" << endl;
};
int main(){
cout << "main-begin" << endl;
func2();
cout << "main-end" << endl;
getchar();
return 0;
}
//输出
main-begin
func2-begin
func1-begin
产生异常了:(int)666
func1-end
func2-end
main-end
异常时严谨匹配，double类型的exception获取不到int类型的异常
图片.png
抛异常在函数捕获终止位置，抛异常后面的代码不会执行
void func1(){
cout << "func1-begin" << endl;
throw 666;
cout << "func1-end" << endl;
};
void func2(){
cout << "func2-begin" << endl;;
func1();
cout << "func2-end" << endl;
};
int main(){
cout << "main-begin" << endl;
try{
func2();
}catch(int exception){
cout << "产生异常了:(int)" << exception << endl;
}
cout << "main-end" << endl;
getchar();
return 0;
}
//输出
main-begin
func2-begin
func1-begin
产生异常了:(int)666
main-end
3.异常的抛出声明
◼ 为了增强可读性和方便团队协作，如果函数内部可能会抛出异常，建议函数声明一下异常类型
图片.png
4.自定义异常类型
//所有异常的基类
class Exception{
public:
virtual const char *what() = 0;
};
class DivideException:public Exception{
public:
const char *what(){
return "不能除以0";
};
int code(){
return 303;;
}
};
class AddException:public Exception{
public:
const char *what(){
return "加法有问题";
};
int code(){
return 202;;
}
};
int divide(int v1,int v2){
if (v2 == 0) {
//抛出异常
throw DivideException() ;
}
return v1/v2;;
}
void test4(){
cout << 1 << endl;
try {
int a = 10;
int b = 0;
cout << divide(a, b) << endl;
} catch (DivideException exception) {
cout << "产生异常了(DivideException) " << exception.what() << endl;
}catch(AddException exception){
cout << "产生异常了(AddException) " << exception.what() << endl;
}
cout << 2 << endl;
}
int main(){
test4();
getchar();
return 0;
}
//输出
1
产生异常了(DivideException) 不能除以0
2
基类异常接收子类的异常，统一接收，不管什么异常都统一接收
class DivideException:public Exception{
public:
const char *what() const{
return "不能除以0";
};
int code() const{
return 303;;
}
};
class AddException:public Exception{
public:
const char *what() const{
return "加法有问题";
};
int code() const{
return 202;;
}
};
int divide(int v1,int v2){
if (v2 == 0) {
//抛出异常
throw DivideException() ;
}
return v1/v2;;
}
void test4(){
cout << 1 << endl;
try {
int a = 10;
int b = 0;
cout << divide(a, b) << endl;
} catch (const Exception &exception) {
cout << "产生异常了(Exception) " << exception.what() << endl;
}
cout << 2 << endl;
}
int main(){
test4();
getchar();
return 0;
}
//输出
1
产生异常了(Exception) 不能除以0
2
5.标准异常(std)
图片.png
图片.png
int main(){
// test4();
cout << 1 << endl;
for (int i = 0; i<999999; i++) {
try {
int *p = new int[9999999];
} catch (bad_alloc exception) {
cout << "产生异常了:内存不够用" << exception.what() <<endl;
break;
}
}
cout << 2 << endl;
}
//输出
1
产生了异常:内存不够用 - bad allocation
2
也可直接使用父类exception
int main(){
// test4();
cout << 1 << endl;
for (int i = 0; i<999999; i++) {
try {
int *p = new int[9999999];
} catch (const exception &exception) {
cout << "产生异常了:内存不够用" << exception.what() <<endl;
break;
}
}
cout << 2 << endl;
}
//输出
1
产生了异常:内存不够用 - bad allocation
2
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