Learning about set jump exceptions

Set jump exceptions may be viewed as C-style exceptions. Like C++-style exceptions, set jump exceptions provide the user with the ability to set a place in the code to return to in the event of an error, and a method for generating the exception that performs the jump. The following code example demonstrates this:

#include <cstring>
#include <csetjmp>

#include <iostream>

std::jmp_buf jb;

void myfunc(int val)
{
    if (val == 42) {
        errno = EINVAL;   // Invalid argument
        std::longjmp(jb, -42);
    }
}

int main()
{
    if (setjmp(jb) == -42) {
        std::cout << "failure: " << strerror(errno) << '\n';
        std::exit(EXIT_FAILURE);
    }

    myfunc(1);
    std::cout << "success\n";

    myfunc(42);
    std::cout << "success\n";
}

// > g++ -std=c++17 scratchpad...