++ val的解释++和++ * p ++用C [英] Explanation of ++val++ and ++*p++ in C
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问题描述
int val = 5;
printf("%d",++val++); //gives compilation error : '++' needs l-value
int *p = &val;
printf("%d",++*p++); //no error
有人能解释一下这两个案例？谢谢你。
Could someone explain these 2 cases? Thanks.
推荐答案
++ VAL ++ 相同 ++（VAL ++）。由于 VAL ++的结果不是左值，这是非法的。正如斯蒂芬佳能指出，如果结果 VAL ++ 是一个左值， ++（VAL ++）将是不确定的行为还有就是 ++ 秒之间没有顺序点。
++val++ is the same as ++(val++). Since the result of val++ is not an lvalue, this is illegal. And as Stephen Canon pointed out, if the result of val++ were an lvalue, ++(val++) would be undefined behavior as there is no sequence point between the ++s.
++ * P ++ 相同 ++（*（P ++））。由于 *（P ++）的结果的是的左值，这是合法的。
++*p++ is the same as ++(*(p++)). Since the result of *(p++) is an lvalue, this is legal.
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