Question

I'm trying the write exception an handling in case a txt file could not be found and open. I'm receiving "terminating with uncaught exception of type char const*" from the compiler. I don't understand why I cannot see the catch message "File could not be opened"

try{

 ins.open(argv[1]);
 if ( !ins )
       throw "not";

} catch (char& e){
   cout << "File could not be opened";
   exit( 1 );
}

Answer 1

"not" is rightly a char array, you have to catch it with catch (const char* e)but this is really a bad way to proceed...

Quick example (source: http://www.tutorialspoint.com/cplusplus/cpp_exceptions_handling.htm)

#include <iostream>
#include <exception>
using namespace std;

struct MyException : public exception
{
  const char * what () const throw ()
  {
    return "C++ Exception";
  }
};

int main()
{
  try
  {
    throw MyException();
  }
  catch(MyException& e)
  {
    std::cout << "MyException caught" << std::endl;
    std::cout << e.what() << std::endl;
  }
  catch(std::exception& e)
  {
    //Other errors
  }
}

Answer 2

@ 56ka的回答是正确的，但为了使异常处理消息更通用，你可以编写构造函数，如下所示。

#include <cmath>
#include <iostream>
#include <exception>
#include <stdexcept>
using namespace std;

//Write your code here
struct MyException : public exception
{
    protected:
    const char *errorMsg;

    public:
    MyException (const char* str){
        errorMsg =  str;    
    }
    const char * what () const throw ()
    {
        return errorMsg;
    }
};

class Calculator
{
    public:

    int power(int n, int p){
        if ( n < 0 || p < 0){
            throw MyException("n and p should be non-negative");
        }
        return pow(n,p);
    }
};

int main()
{
    Calculator myCalculator=Calculator();
    try{
        int ans=myCalculator.power(2,-2);
        cout<<ans<<endl; 
    }
    catch(exception& e){
         cout<<e.what()<<endl;
    }

}

Answer 3

Better to throw std::ios_base::failure (C++11) or something else that derives from std::exception. Don't write your own exception classes unless you really have to. It's cleaner to use the existing exceptions defined by the standard library.

terminating with uncaught exception of type

3 个答案: