CODEWITHSUNDEEP
c++c++11compilationruntime
RaGa__M
RaGa__M

Reputation: 2569

which system software is responsible for Run time check

I thought this would sound a general simple question but I got up this when reading C++ exception specification. that said in one of the book, C++11 now have a keyword 'noexcept' that means no exception will be thrown from a function when it is declared with the function header and that said the reason for this keyword came into existence is C++ exception specifications are checked at run time rather than at compile time, so they offer no programmer guarantees that all exceptions have been handled. and hence they conclude two case a function would throw exception or if we are clear if it will never throw, then use noexcept for optimization(hopefully)

void foo() noexcept();

Here is the main question. Which system software perform those run time checking(I hope not compiler/linker/loader) and also which system software is responsible for allocating memory at run time(dynamic memory allocation) when this are all not taken care by compiler and others?

Upvotes: 2

Views: 125

Answers (4)

Chris Beck
Chris Beck

Reputation: 16204

Indeed, you would not say that the "standard library" handles this. Exceptions and exception specifications are rather a core language feature, more fundamental than the standard library.

You could similarly ask, what piece of software ensures that when I call a function in C++, that the caller actually receives the values that I pass in? What piece of software manipulates the stack frame pointers while my program is running?

From the point of view of the standard I would say "the implementation" is responsible for these details. In some languages, like Java for instance, there is a "Java Runtime Environment" which is very clearly responsible for these things, and you could try to study exactly how it does them. In C++ there is no universal runtime environment -- like others have said, the compiler is responsible to generate code that ensures that these things happen, and that code ends up sprinkled throughout your resulting executable. How exactly the compiler achieves its task is implementation-specific, you can't give a general answer beyond what the standard says, and generally it specifies the expected behavior, not the details under the hood.

When you ask

also which system software is responsible for allocating memory at run time(dynamic memory allocation

this is again an implementation detail, it will differ from compiler to compiler.

Upvotes: 1

MSalters
MSalters

Reputation: 180020

Typically the responsible software isn't one clearly identifiable piece of code, but small fragments of code sprinkled through the executable. The compiler translates your code into binary instructions, and noexcept is no exception ;).

Upvotes: 2

kfsone
kfsone

Reputation: 24269

There is no active "system software" checking for exceptions, as you phrase it; rather, throwing an exception is an action taken by the program itself. The program passes the exception back up the stack until the exception matches an exception handler.

If no exception handler matches, then the exception is caught by the bootstrap code (main is not the actual entry point for a typical program, but is where the runtime hands control to the programmer) and the program terminates.

Upvotes: 3

EmDroid
EmDroid

Reputation: 6046

AFAIK this is done by the C++ runtime (libstdc++ for example). In case of exceptions, there are some guards added around the functions by the compiler (this is necessary anyway to call destructors in case exception is thrown), and in the case of noexcept, if the function throws (or if it throws other exception than advertised by the throw() specification), terminate() is called by the C++ runtime and the application is shut down.

Memory heap allocations are also (by default) done by the C++ runtime libraries.

Upvotes: 2

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