C++異常的常用實例(C++ Exception)

本文收集了有關C++異常的常用實例，附精簡代碼。

關鍵詞：C++異常  C++ Exception try/catch throw

• 異常捕獲：使用try/catch捕獲異常。

 
#include <iostream> 
#include <string> 
#include <stdexcept>  
int main() {   
   std::string str("foo");      
   try {       
      str.at(10); // access element, may throw std::out_of_range   
   } catch (const std::out_of_range& e) {       
      // what() is inherited from std::exception and contains an explanatory message       
      std::cout << e.what();  
   } 
}

• 連續多個異常捕獲

 std::string str("foo");    
 try {     
   str.reserve(2); // reserve extra capacity, may throw std::length_error     
   str.at(10); // access element, may throw std::out_of_range 
 } catch (const std::length_error& e) {     
   std::cout << e.what(); 
 } catch (const std::out_of_range& e) {
   std::cout << e.what(); 
 } catch (const std::exception& e) {     
   std::cout << e.what(); 
 }

• 捕獲任意異常/捕獲所有異常，或者叫匿名捕獲異常

 try {
     throw 10; 
 } catch (...) {     
     std::cout << "caught an exception"; 
 }

• 異常捕獲最佳實踐：拋出異常值，捕獲異常值的引用，可以避免不必要的開銷。

 try {     
 // throw new std::runtime_error("Error!");   
 // Don't do this!     
 // This creates an exception object     
 // on the heap and would require you to catch the     
 // pointer and manage the memory yourself. This can     
 // cause memory leaks!          throw std::runtime_error("Error!"); 
 } catch (const std::runtime_error& e) {     
    std::cout << e.what() << std::endl; 
 }

• 將異常簡單處理之後，繼續拋出

try {  
     ... // some code here 
} catch (const SomeException& e) {
     std::cout << "caught an exception";
     throw; 
}

• 自定義C++異常

#include <exception>  
class Except: virtual public std::exception {      
protected:
     int error_number;               ///< Error number
     int error_offset;               ///< Error offset
     std::string error_message;      ///< Error message
public:      
/** Constructor (C++ STL string, int, int).      
*  @param msg The error message      
*  @param err_num Error number      
*  @param err_off Error offset      
*/     
explicit Except(const std::string& msg, int err_num, int err_off): 
         error_number(err_num), error_offset(err_off),error_message(msg)         {}      
/** Destructor.      
*  Virtual to allow for subclassing.      
*/     
virtual ~Except() throw () {}      
/** Returns a pointer to the (constant) error description.      
*  @return A pointer to a const char*. The underlying memory      
*  is in possession of the Except object. Callers must      
*  not attempt to free the memory.      
*/     
virtual const char* what() const throw () { 
       return error_message.c_str();     
}          
/** Returns error number.      
*  @return #error_number      
*/     
virtual int getErrorNumber() const throw() {         return error_number;     }          
/**Returns error offset.      
* @return #error_offset      
*/     
virtual int getErrorOffset() const throw() {         return error_offset;     }  
}; 

• 拋出上述自定義異常

try {     
   throw(Except("Couldn't do what you were expecting", -12, -34)); 
} catch (const Except& e) {     
   std::cout<<e.what() <<"
   Error number: "<<e.getErrorNumber() <<"
   Error offset: "<<e.getErrorOffset(); 
}