Warn about do nothing expressions?

[Ali Çehreli]

On 03/28/2014 01:59 PM, Justin Whear wrote:

 > $ clang test.c && ./a.out
 > test.c:7:7: warning: multiple unsequenced modifications to 'i' [-
 > Wunsequenced]
 >          i = i++;
 >            ~  ^
 > 1 warning generated.
 > 0
 >
 >
 > Both gcc and clang agree that in C, assigning a post-increment to itself
 > results in the original value.

The result of a test program cannot be proof of that. In fact, changing 
the value of a variable more than once between two sequence points is 
undefined behavior.

 > At least Clang warns, which is good,

It is unfortunate that Clang does not use the word "undefined" there.

 > but D is consistent with C's behavior on this point.

It is undefined behavior in both languages.

Ali