int x = x;
I know it is UB, but I'd like to known what prevents the language to forbid that in the first place. Is it because it is equivalent to
int x;
x = x;
?
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2On what are you basing the fact that there's any reason for it to be syntactically invalid? – Thomas Jager Jun 24 '19 at 19:49
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5please choose one language. C and C++ have diverged long time ago and do not have the same rules concerning ub – 463035818_is_not_an_ai Jun 24 '19 at 19:51
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2I suspect that not permitting it would also break idiomatic constructs like `int *x = malloc(sizeof *x);`. – Shawn Jun 24 '19 at 19:51
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so that you can write x=x+1 for example – macroland Jun 24 '19 at 19:52
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2Completely legal constructs include `x = sizeof(x);`, `void *p=&p`, but I agree that the compiler should be able to tell the difference. – Gem Taylor Jun 24 '19 at 19:56
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Also related but [not quite a dup](https://stackoverflow.com/questions/14935722/does-initialization-entail-lvalue-to-rvalue-conversion-is-int-x-x-ub) – 1201ProgramAlarm Jun 24 '19 at 19:57
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1fwiw [this answer](https://stackoverflow.com/a/42365867/4117728) mentions one case where `int i =i;` is not undefined – 463035818_is_not_an_ai Jun 24 '19 at 20:01