C 中的逗号和赋值运算符

Question

我有以下内容:

int a = 1, b = 2, c = 3, d = 4;
a = b, c = d;
printf("%d, %d, %d, %d", a, b, c, d);

输出是:

2, 2, 4, 4

逗号运算符如何与赋值运算符一起使用？据我所知，如果我们有，它将评估并返回第二个表达式，

(exp1, exp2)

那么，它为什么要评估 a = b ？

Answer 1

计算第一个操作数并丢弃结果。然后计算第二个操作数，并将结果作为表达式的总结果返回。

标准说:

The left operand of a comma operator is evaluated as a void expression; there is a sequence point between its evaluation and that of the right operand. Then the right operand is evaluated; the result has its type and value.