Pre & post increment operator behavior in C, C++, Java, & C#
This question already has an answer here:
Java and C# evaluate expressions from left to right, and the side-effects are visible immediately.
In C++, the order of evaluation of subexpressions is unspecified, and modifying the same object twice without an intervening sequence point is undefined behavior.
I don't have the time to write up a detailed description of the differences between C++, C, C# and Java. I will merely say that the C# behaviour of the pre and post increment operators is fully specified (in single-threaded scenarios; if you want to know about its atomicity, guarantees about observations of read and write orders in multi-processor weak memory models and so on, you're on your own to do that research.) It is not fully specified in C and C++; a compiler has broad lattitude to do whatever it pleases with re-ordering side effects. I have never used Java so I'm not going to hazard a guess as to what Java does.
For more information on what C# does you should read the C# specification. For a short take on it, read my answer to this question:
What is the difference between i++ and ++i?
For an even shorter take:
Subexpressions in a C# expression are logically grouped by precedence and associativity, and then evaluated from left to right regardless. (So for example, A() + B() * C() evaluates A(), then B(), then C(). The fact that the multiplication "comes before" the addition is irrelevant; the subexpressions are always evaluated left to right.)
If the evaluation of a subexpression causes a side effect because of a pre or post increment subexpression then the side effect happens immediately before the result is produced.
In C++, this is undefined behaviour, so any answer would be correct. See Undefined behavior and sequence points for further details.
Not sure about other languages, but I would expect this code to be incorrect there, too.
EDIT:
See Eric Lippert's answer about C#. He disproves my assumption about C#'s behaviour.
上一篇: 运算符优先级，哪个结果是正确的？