CODEWITHSUNDEEP
c#c++memory-managementdynamic-memory-allocation
Sarfaraz Nawaz
Sarfaraz Nawaz

Reputation: 361472

new never fails?

In C++, we usually see and write code like,

Sample sample=new Sample();
if ( sample == NULL )
{
     std::cout<<"Memory allocation failed" << std::endl;
}

But in C#, I rarely see this: (at least I've never seen this)

Sample sample = new Sample();
if ( sample == null )
{
     Console.WriteLine("Memory allocation failed\n");
}

Means, in C#, we rarely check if a new failed or not. Why is it so? Does it have something to do with "In C#, new never fails"? Is there such a thing in C# that new never fails?

If it fails, then why such "check" is so rare in C#? I'm not talking about OutOfMemoryException, that is after all exception, not "check". I'm talking about the coding style.

Upvotes: 5

Views: 4020

Answers (10)

Prasoon Saurav
Prasoon Saurav

Reputation: 92864

In C++, unlike malloc, new doesn't return NULL on failure. In fact, it throws a std::bad_alloc exception on failure.

If you want new to return NULL on failure, you have to explicitly tell it not to throw an exception. Use std::nothrow version for that purpose. (header file : <new>)

Upvotes: 6

UmmaGumma
UmmaGumma

Reputation: 5693

According to msdn

If the new operator fails to allocate memory, it throws the exception OutOfMemoryException.

http://msdn.microsoft.com/en-us/library/51y09td4%28v=vs.71%29.aspx

By the way, only old C++ compilers return 0 when they trying to allocate memory. Modern ones throwing std::bad_alloc exception. If you wish old behavior you need to write 

Sample sample=new(std::nothrow) Sample();

Upvotes: 15

rve
rve

Reputation: 6055

In C++ new can return NULL when using a non compliant compiler (see Will new return NULL in any case?)

But, the proper way in C++ is that new throws an exception when out of memory, just like C#.

The check for NULL is only needed on certain compilers.

Upvotes: 1

Jacob Relkin
Jacob Relkin

Reputation: 163248

If new fails, then there will be an OutOfMemoryException thrown.

So the equivalent of the C++ code you have would be this:

try { 
  Sample sample = new Sample();
} catch(OutOfMemoryException e) {
  Console.WriteLine("Memory allocation failed\n");
}

Upvotes: 5

Yakov Galka
Yakov Galka

Reputation: 72479

Sample sample=new Sample();
if ( sample == NULL )
{
     // You will never get here!
     std::cout<<"Memory allocation failed" << std::endl;
}

We don't write this in C++ either. "Memory allocation failed" will never appear. In both languages you get an exception if the allocation fails. In C++ it's std::bad_alloc, in C# it's OutOfMemoryException.

Upvotes: 5

bdonlan
bdonlan

Reputation: 231163

In C#, new throws an OutOfMemoryException if it fails, so a NULL check is not necessary.

Incidentally, the same applies in C++ as well - new throws std::bad_alloc if it fails, so there really is no need to test against NULL in C++ either.

Upvotes: 12

Elalfer
Elalfer

Reputation: 5338

  1. I rarely see it in C++
  2. It doesn't make sense in C#, because it simply will just throw an Exception

Upvotes: 1

EboMike
EboMike

Reputation: 77752

Is this some test code you wrote? If so, I assume that you don't actually keep the reference to the object you created, meaning that the garbage collection will kick in and delete some of the objects you created previously.

That said, you can certainly run out of memory if you allocate enough memory and do keep references to it (at which point an exception will be thrown - a NULL pointer as a return value for memory allocations is more common in C, and in C++ versions written for video game consoles.)

Upvotes: 0

jgauffin
jgauffin

Reputation: 101150

There are an OutOfMemoryException in C#

Upvotes: 1

tenor
tenor

Reputation: 1105

new can certainly fail.

Constructors are allowed to throw exceptions. You can also run out of memory when creating a new object.

Upvotes: 1

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