i == (i = 2) 的结果是什么?
2022-09-01 00:57:08
以下代码如下:
// In Java, output #####
public static void main(String[] args) {
int i = 1;
if(i == (i = 2)) {
System.out.println("@@@@@");
} else {
System.out.println("#####");
}
}
但:
// In C, output @@@@@,I did test on Clion(GCC 7.3) and Visual Studio 2017
int main(int argc, char *argv[]) {
int i = 1;
if(i == (i = 2)) {
printf("@@@@@");
} else {
printf("#####");
}
return 0;
}
提出这个问题的动机来自以下代码:
// The code is from the JDK 11 - java.util.concurrent.atomic.AtomicInteger
// I am curious about the behavior of the variable prev.
public final int getAndUpdate(IntUnaryOperator updateFunction) {
int prev = get(), next = 0;
for (boolean haveNext = false;;) {
if (!haveNext)
next = updateFunction.applyAsInt(prev);
if (weakCompareAndSetVolatile(prev, next))
return prev;
haveNext = (prev == (prev = get()));
}
}
那么,如何解释以上两种不同的执行模式呢?