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+---- Thread: Rule 0.1.9 - is zero-initialization considered "dead code"? (/showthread.php?tid=1705)
Rule 0.1.9 - is zero-initialization considered "dead code"? - cgpzs - 25-09-2024
Consider the following example:
Code:
// third_party.h
struct Foo
{
int32_t a;
int32_t b;
};
// client.cpp
Foo create()
{
Foo f{}; // Violates Rule 0.1.9?
f.a = 123;
f.b = 321;
return f;
}Does that violate Rule 0.1.9? While the initialization may be redundant, it serves a purpose as defensive programming. If we remove the zero-initialization, we risk having some members of "Foo" uninitialized, especially if we bump to a new version of "third_party.h" that adds a new member to the struct. It's safer to zero-initialize at the declaration, to ensure no members remain uninitialized.
It's also preferable to initialize like this instead of "Foo f{123, 321};", because we can see written in code which field gets which value. We need to wait until C++20 to get designated initializers in C++ to initialize everything in one line.
Thanks!
RE: Rule 0.1.9 - is zero-initialization considered "dead code"? - misra cpp - 27-09-2024
Strictly this does not violate 0.1.9, because the statement that declares f cannot be removed and still leave working code, but it may be seen as zero initialising followed by assignment (i.e. the zero initialisation is redundant) which violates 0.1.6.
RE: Rule 0.1.9 - is zero-initialization considered "dead code"? - cgpzs - 27-09-2024
Thanks, it appears that my static analyzer mistakenly mapped the error message to 0.1.9.
I read now the discussion about 0.1.6:
https://forum.misra.org.uk/showthread.php?tid=1522
MISRA have previously stated that 0.1.6 is intended for DU anomalies only, so it does not appear this case falls under that category?
I also note that MISRA C++ 2023, rule 0.1.1, function f5() marks a very similar example as compliant. Is that also compliant under MISRA C++:2008?
RE: Rule 0.1.9 - is zero-initialization considered "dead code"? - misra cpp - 11-10-2024
You're right, your example should be compliant in both 2008 & 2023.
However, we think we've made a mistake in not allowing overwriting zero initialisation
This will be clarified in the next edition.