*(p+5) 和 p[5] 执行效率不一样么？Linux内核里有这样用指针的么？

iw1210

*(p+5) 和 p[5]  执行效率不一样么？Linux内核里有这样用指针的么？

int main(void)

{
        int      n= 23;
        void**   p;

        p = malloc(10*sizeof(void*));
        *(p+5) = &n;
        p[5] = &n;
        printf("*(*(p+5)) = %d\n",*((int*)*(p+5)));
        printf("*(p[5])=%d\n",*((int*)p[5]));
        free(p);
        system("pause");
}

mymtom_cu

*(p+5)与p[5]一模一样！

C89

3.3.2.1 Array subscripting
Constraints

One of the expressions shall have type “pointer to object type,” the other expression shall have integral type, and the result has type “ type.”
Semantics

A postfix expression followed by an expression in square brackets [] is a subscripted designation of a member of an array object. The definition of the subscript operator [] is that E1[E2] is identical to (*(E1+(E2))). Because of the conversion rules that apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the initial member of an array object) and E2 is an integer, E1[E2] designates the E2 -th member of E1 (counting from zero).

iw1210

回复 2# mymtom_cu


    谢谢，我喜欢p[5]表达，容易阅读，大家喜欢那种表达？

linux_c_py_php

如果是&p[5], 那应该考虑直接p+5了, 其他情况随意.

liuiang

楼主先是问了一大堆应用程序问题，搞的应用工程师痛不欲生，

然后开始攻击数学，搞的算法工程师痛不欲生，

现在开始搞内核，楼主，我也搞点内核得东西，求您高抬贵手，把内核当个屁给放了吧~~~~~~

iw1210

回复 5# liuiang


    只问问内核里用没有这么用指针的，没搞内核

zylthinking

liuiang 发表于 2013-02-05 16:11
楼主先是问了一大堆应用程序问题，搞的应用工程师痛不欲生，

然后开始攻击数学，搞的算法工程师痛不欲生 ...

把他当个屁给放了吧

w_anthony

回复 5# liuiang


    一针见血

lxyscls_cu

跟内核有个屁关系

编译器当成一样就一样{:3_188:}