At that point, if the test returns true, you launch your exception. The way (at least in my time) in C++ (or in any of the languages I've mentioned) was to explicitly check if the pointer (or the address being assigned to a reference) was null. If the JVM weren't programmed to do such a thing, an access to a null reference would cause the JVM to crash with a SEGFAULT - exactly the behavior one would expect with a compiled, unguarded language when encountering an unguarded null pointer de-referencing (not just C or C++ but also in Pascal, Ada, Assembly or even good old BASIC attempting to do a PEEK/POKE at an invalid address location.) The JVM always check (internally) if the reference is null, and when it finds that it is, it automatically throws a. In Java, a call to de-reference a reference is ultimately a bytecode instruction sent and interpreted by the JVM. You have to be a lot, lot, but lot more proactive in checking for errors (and in throwing your own custom exceptions).
The exception model in C++ is very different from the one in Java. So much has changed with the STL and C++ that maybe things have changed. Take it with a grain of salt because I haven't touched a C++ compiler since 1999.
#NULL POINTER EXCEPTION ERROR PARALLELS TOOLBOX SOFTWARE#
You will not in general get a C++-style software exception that you can catch with any kind of catch clause, although Windows does have a feature called SEH which you can use to get that behavior. So on most systems, most of the time, when you dereference a null pointer you'll get some kind of hardware exception or signal, or your process will be killed, or perhaps on an embedded system the device will lock up and need a reboot. In practice of course, compilers have good reasons not to set your computer on fire, and modern OSes try to ensure that badly-behaved apps don't massively inconvenience other apps. C++ functions with pointer parameters should document whether or not null pointers are permitted.ĭifferent people will write the test (s=0) differently - it could be (s=NULL) or (NULL=s) or (!s). Your function could be rewritten: int my_function(const char* const s)Īlternatively you could fix the caller to not pass a null pointer in the first place, or you could fix do_something_with to accept a null pointer. Of course it's difficult to avoid errors in the first cut of your code, so when you do it by accident and your computer doesn't catch fire, then you were lucky, fix the bug and move on. In general it's best to assume that undefined behavior will cause your computer to catch fire (or format the hard disk). If it doesn't, the behavior might be consistent and predictable, or it might not. Anything is permitted - a particular implementation might document its own behavior, or it might not. This means the C++ standard doesn't put any limits on what may happen. Dereferencing a null pointer in C++ is undefined behavior.
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