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The answer seems to be to use std::nothrow, which looks like: [0] int *p = new (std::nothrow) int[5]; // gives null if alloc fails A related question: Many

The answer seems to be to use std::nothrow, which looks like: [0] int *p = new (std::nothrow) int[5]; // gives null if alloc fails A related question: Many C++ coding standards, including Google's, prohibit use of C++ exceptions. Do they have to use the nothrow syntax everywhere the new operator is used? [0] https://www.cplusplus.com/reference/new/operator%20new[]/ https://www.cplusplus.com/reference/new/operator%20new[]/

jfkebwjsbx 7y ago
You can also abort the program, which is what most programs do on OOM anyway.
twic 7y ago
My guess would be that they lean on the fact that "malloc never fails" [1]. Under that model, new and malloc always give you a pointer you can use, it's just that sometimes, using it will give you a segfault. [1] https://scvalex.net/posts/6/ https://scvalex.net/posts/6/
- MaxBarraclough 7y ago
  That blog post describes Linux's default 'memory overcommitment' behaviour. Oddly it fails to mention the term 'overcommit'. As the post says, malloc can return null even where overcommit is used; it's not true that malloc never fails when overcommit is enabled. Even if it were true that malloc/calloc/realloc/new/new[] could never fail on your OS+compiler, it doesn't seem wise to write code that relies on that non-standard guarantee. Poor robustness and portability.
saagarjha 7y ago
Not a Googler, but I believe that exceptions coming from the standard library (which must support exceptions, of course…) are allowed.
- klodolph 7y ago
  Various folks working on C++ tooling at Google and e.g. Abseil have commented in talks—no, the standard library is not required to support exceptions. They are in fact disabled. Code which would throw an exception instead aborts the program.
  - saagarjha 7y ago
    Ah, I see that Microsoft's implementation does allow this. I wonder if you could still call that standards compliant?
    - klodolph 7y ago
      The C++ requires exceptions, so with -fno-exceptions, the compiler is not standards compliant. However, the big companies like Apple, Facebook, and Google simply don’t care about standards compliance in their internal C++ code bases. At least, not as an end goal. There are a lot of good talks about this.
klodolph 7y ago
Instead of throwing, you just abort the program. If you are running part of a backend service this is reasonable, under some assumptions. If you fail to allocate memory, there’s a good chance that your process can’t continue servicing requests anyway. So, it’s a good tradeoff to abort. The client can retry later or with a different backend, and the job scheduler can start another instance of the process.

jfkebwjsbx 7y ago

You can also abort the program, which is what most programs do on OOM anyway.

twic 7y ago

My guess would be that they lean on the fact that "malloc never fails" [1]. Under that model, new and malloc always give you a pointer you can use, it's just that sometimes, using it will give you a segfault. [1] https://scvalex.net/posts/6/ https://scvalex.net/posts/6/

MaxBarraclough 7y ago
That blog post describes Linux's default 'memory overcommitment' behaviour. Oddly it fails to mention the term 'overcommit'. As the post says, malloc can return null even where overcommit is used; it's not true that malloc never fails when overcommit is enabled. Even if it were true that malloc/calloc/realloc/new/new[] could never fail on your OS+compiler, it doesn't seem wise to write code that relies on that non-standard guarantee. Poor robustness and portability.

saagarjha 7y ago

Not a Googler, but I believe that exceptions coming from the standard library (which must support exceptions, of course…) are allowed.

klodolph 7y ago
Various folks working on C++ tooling at Google and e.g. Abseil have commented in talks—no, the standard library is not required to support exceptions. They are in fact disabled. Code which would throw an exception instead aborts the program.
- saagarjha 7y ago
  Ah, I see that Microsoft's implementation does allow this. I wonder if you could still call that standards compliant?
  - klodolph 7y ago
    The C++ requires exceptions, so with -fno-exceptions, the compiler is not standards compliant. However, the big companies like Apple, Facebook, and Google simply don’t care about standards compliance in their internal C++ code bases. At least, not as an end goal. There are a lot of good talks about this.

klodolph 7y ago

Instead of throwing, you just abort the program. If you are running part of a backend service this is reasonable, under some assumptions. If you fail to allocate memory, there’s a good chance that your process can’t continue servicing requests anyway. So, it’s a good tradeoff to abort. The client can retry later or with a different backend, and the job scheduler can start another instance of the process.