C Throw exception in constructor-CodePudding

class MyClass {
    
    std::string filename;

public:
    MyClass(std::string new_filename);
    ~MyClass();
}

MyClass.hpp

#include <MyClass.hpp>

MyClass::MyClass(std::string new_filename) {

   filename = new_filename;
}

MyClass::~MyClass() {};

MyClass.cpp

I want the constructor only to run when the filename is of a correct form. E.g.: "Name.aa.js".

I tried it with exception handling but I don't quite understand how to use it correctly. I have a function that checks whether the given string parameter is of the correct form.

static bool MyClass::is_filename(std::string name) {

   if (regex_match(name, std::regex("(Name.)[a-z]{2}(.js)"))) {
       
       return true;
   }
   return false;
}

And then I put

if (!is_filename(new_filename)) {

   throw;
}

at the beginning of my constructor. When I run my Code with a wrong filename it just outputs "Debug Error", but works with a correct filename. I also tried

throw std::invalid_argument;

But it says

base of all invalid-argument exceptions

no instance of constructor 'std::invalid_argument::invalid_argument' matches the argument list

Where and how exactly do I have to use the throw argument? Do I need to implement try / catch aswell for this to work?

CodePudding user response：

std::invalid_argument has no default constructor (one that can be called without parameters). There are two constructors taking a message (either as const char* or std::string):

throw std::invalid_argument("wrong filename");

Where and how exactly do I have to use the throw argument?

When an object cannot be constructed then the constructor is the right place to throw an exception.

Do I need to implement try / catch aswell for this to work?

Depends. You need no try/catch to throw an exception, but if the exception is not caught then your program will terminate.

CodePudding user response：

throw std::invalid_argument("Invalid argument."); would work. The constructor requires an argument to be passed.

You'll need to catch the exception though somewhere further up the call stack. Do that with

try {
    // your function here
} catch (const std::exception& e){
    // deal with the exception here, use e.what() to extract the message
}

Alternatively, you can catch std::invalid_argument or std::logic_error depending on how generic you want to be.

Note that throw; on its own can be used at a catch site to throw the current exception by reference. It is the only nullary operator in C .