用noexcept C ++ 11正确实现功能

Question

Are those functions correctly implementing noexcept / throw()

Fisrst function

void do_something(const std::string s) noexcept{
    // do something with no exception
}

do_something("Hello");

"Hello" literal will create new std::string object and it might throw an exception.

Is this exception will be thrown outside of the function or inside?

Second function:

size_t do_something(const char *s) noexcept{
    return strlen(s);
}

do_something(nullptr);

strlen is chosen because it is legacy C function and it will crash, because s is nullprt .

However this crash is nothing to do with exceptions. Is the assumption correct?

Answer 1

In:

void do_something(const std::string s) noexcept

The argument s is constructed by the caller. That is, if constructing std::string throws an exception, that exception is thrown before do_something is called.

---

strlen is chosen because it is legacy C function and it will crash, because s is nullptr .

Technically, accessing memory through invalid pointers results in undefined behaviour. No C++ exceptions are thrown in such cases and the compiler/run-time are not required to detect that.

Unlike Java which throws NullPointerException . Those Java checks for null pointers may be cheap, but they are not free.

On Linux/Unix you are most likely to get SIGSEGV signal whose default behavior is to terminate the process. You could install your own signal handler and make it throw a C++ exception, but that would result in even more undefined behaviour.

So, it is best if it crashed as early and loudly as possible so that the code is fixed.

However this crash is nothing to do with exceptions. Is the assumption correct?

Correct, a crash is not an exception. A crash can be caused by an exception though.