Custom exception in C++ for invalid input to a function

Question

I would like to write a custom Error class in C++. I am mostly used to Java (not used them a lot) so I would like to check here if my thought process on how to do this in C++ is correct.

Currently I got the following code:

class InvalidInput : public std::runtime_error { public: InvalidInput(const char* msg) : std::runtime_error(msg) { } };

I plan on using the cutsom error in a function as so:

myFunc(int x) { if (valueIsInvalid(x)) { throw InvalidInput ("invalid input"); } }

Before implementing it I would like to know if I am on the right track on how this should be done in C++ (as well as best practice). If there is a better way feel free to tell me as well.

Unlike Java, exceptions should be used sparingly in C++. Throwing an exception in C++ is expensive, and should be used only for truly exceptional cases. For input validation en exception should typically only be thrown if the program can't really continue anymore. — Some programmer dude
– Some programmer dude, Commented Dec 2, 2019 at 7:48
Regarding the comment by @Evg, you could also use struct instead of class, as then members will be public by default. — Some programmer dude
– Some programmer dude, Commented Dec 2, 2019 at 7:49
@Someprogrammerdude I would consider human input as so slow (compared to speed of computations) that I wouldn't be afraid about performance impact too much (in this case). — Scheff's Cat
– Scheff's Cat, Commented Dec 2, 2019 at 7:50
@DanielsaysreinstateMonica that error class looks like it is meant for input which causes problems with logic. Wrong input in this case will not result in a logic error but will not abide to business rules. — SecretIndividual
– SecretIndividual, Commented Dec 2, 2019 at 7:55

Bharat Vankar · Accepted Answer · 2019-12-02 11:04:13Z

For your solution as below.

create custome exception

class InvalidInput : public std::exception{ public: InvalidInput(std::string msg):errorMsg_(msg){} virtual const char* what() const throw() { return errorMsg_; } private: std::string errorMsg_; };

use of that custome excetion

myFunc(int x) { if (valueIsInvalid(x)) { throw InvalidInput ("invlaid input"); } }

You can complete your answer by mentioning that it is possible to const char* what() override

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