CODEWITHSUNDEEP
c++exceptionerror-handling
Jimmy
Jimmy

Reputation: 925

C++ Exception - Throw a String

I'm having a small issue with my code. For some reason, when I try to throw a string with the code below, I get an error in Visual Studio.

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

int main()
{
    
    char input;

    cout << "\n\nWould you like to input? (y/n): ";
    cin >> input;
    input = tolower(input);

    try
    {
        if (input != 'y')
        {
            throw ("exception ! error");
        }
    }
    catch (string e)
    {
        cout << e << endl;
    }
}

Error :

error

Upvotes: 21

Views: 52424

Answers (4)

Aarya Ningaraddiyavar
Aarya Ningaraddiyavar

Reputation: 1

try
{
  if (input != 'y')
  {
    string error = "exception ! error";
    throw error;
  }
}

When you put a string in "" it is considered as a string of characters, instead assign it to a string class variable.

Upvotes: -1

Mr.C64
Mr.C64

Reputation: 42924

Throwing a string is really a bad idea.

In your code you are throwing a const char*. Throwing a built-in type (like an int, or float, or a const char* like in this case) is a bad idea because these built-in types don't carry proper contextual error information. In fact, when an exception is caught, it's important to understand the reason for the exception to take proper action. But a built-in type doesn't properly provide such information, making it difficult at the catch-site to understand the reason and the cause for the exception.

Moreover, throwing a built-in type is also confusing, as it's not idiomatic modern C++. The idiomatic C++ way of throwing an exception is to define a proper C++ class to represent the exception, typically deriving it from std::exception, or from some other class derived from std::exception, and then throw an instance of such exception class. You could also simply throw some of the C++ exception classes already defined in the C++ Standard Library, like std::runtime_error.

For example, you could throw a std::runtime_error, passing an error message string to the constructor, like this:

throw std::runtime_error("Your error message");

and, at the catch site, you can catch the runtime_error exception by const reference (const &), and invoke the what() method to get the error string.

try {
    ...
} catch (const std::runtime_error& ex) {
    // Invoke ex.what() to get the error message
}

But do not throw the "naked" string.

In case you want to define a custom exception class, you can derive it for example from std::runtime_error like this:

class YourCustomException
    : public std::runtime_error 
{
  public:

    YourCustomException(const char* message)
        : std::runtime_error(message) {
    }

    YourCustomException(const std::string& message)
        : std::runtime_error(message) {
    }
};

throw it like this:

throw YourCustomException("Your error message");

and catch it like this:

try {
    ...
} catch (const YourCustomException& ex) {
    // Invoke ex.what() to get the error message
}

Upvotes: 28

AzKaR
AzKaR

Reputation: 51

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

int main()  
{
    
    char input;

    cout << "\n\nWould you like to input? (y/n): ";
    cin >> input;
    input = tolower(input);

    try
    {
        if (input != 'y')
        {
            throw std::runtime_error("Exception ! Error");
        }
    }

    catch(const std::exception& e)
    {
        std::cout << "Caught exception: " << e.what() << '\n';
    }
}

Upvotes: 3

Syntactic Fructose
Syntactic Fructose

Reputation: 20076

You are currently throwing a const char* and not a std::string, instead you should be throwing string("error")

edit: the error is resolved with

throw string("exception ! error");

Upvotes: 24

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