c - 了解逗号运算符

Question

int main()
{
    int a = (1,2,3);
    int b = (++a, ++a, ++a);
    int c= (b++, b++, b++);
    printf("%d %d %d", a,b,c);
}

我是编程初学者。我不明白这个程序如何显示 6 9 8 的输出。

Answer 1

三个声明中都使用了,

int a = (1,2,3);
int b = (++a, ++a, ++a);
int c = (b++, b++, b++);  

是comma operator .它计算第一个操作数¹ 并将其丢弃，然后计算第二个操作数并返回其值。因此，

int a = ((1,2), 3);          // a is initialized with 3.
int b = ((++a, ++a), ++a);   // b is initialized with 4+1+1 = 6. 
                             // a is 6 by the end of the statement
int c = ((b++, b++), b++);   // c is initialized with 6+1+1 = 8
                             // b is 9 by the end of the statement.

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_{1 在逗号运算符的情况下，保证从左到右计算顺序。}