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C语言中有个类型限定符restrict，谁能解释下这个限定符的含义！

楼主piaozi2003（）2005-12-12 13:46:35 在 C/C++ / C语言提问

如题问题点数：50、回复次数：12Top

1 楼piaozi2003（）回复于 2005-12-12 13:52:58 得分 0

自己先顶!Top

2 楼improgrammer（无忌）回复于 2005-12-12 14:08:06 得分 0

答案是：标准C语言没有这个关键字。Top

3 楼happy__888（[顾问团]寻开心 www.e-jjj.com）回复于 2005-12-12 14:08:58 得分 0

没有听说这个关键字
不是标准cdTop

4 楼piaozi2003（）回复于 2005-12-12 14:24:43 得分 0

有这个呀Top

5 楼piaozi2003（）回复于 2005-12-12 14:27:14 得分 0

在UNIX下的strtok函数原型是

char* strtok(char* restrick s1, const char* restrict s2)Top

6 楼megaboy（飞天御剑流之杀神一刀斩）回复于 2005-12-12 14:30:13 得分 20

restrict关键字从C99才开始支持，C89是没有的：

6.7.3 Type qualifiers

Syntax

type-qualifier:
const
restrict
volatile

Constraints
Types other than pointer types derived from object or incomplete types shall not be
restrict-qualified.Top

7 楼piaozi2003（）回复于 2005-12-12 14:31:55 得分 0

我在网上只查到这么点资料

关键字restrict用来消除数据间的相关性，编译器从而可以安排语句的并行执行；

但不是很理解，所以在这里请教！而且我在网络上查到好多C语言的书中目录中都有
关于restrict的介绍，所以谁知道的话请说说Top

8 楼megaboy（飞天御剑流之杀神一刀斩）回复于 2005-12-12 14:35:34 得分 0

restrict表示只能通过它限定的指针访问该指针所指向的对象。Top

9 楼megaboy（飞天御剑流之杀神一刀斩）回复于 2005-12-12 14:38:33 得分 0

7 An object that is accessed through a restrict-qualified pointer has a special association with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to that object use, directly or indirectly, the value of that particular pointer. The intended use of the restrict qualifier (like the register storage class) is to promote optimization, and deleting all instances of the qualifier from all preprocessing translation units composing a conforming program does not change its meaning (i.e., observable behavior).Top

10 楼wanguodu（足文字D）回复于 2005-12-12 16:19:34 得分 30

看看TI的帮助：
To help the compiler determine memory dependencies, you can qualify a pointer, reference, or array with the restrict keyword. The restrict keyword is a type qualifier that may be applied to pointers, references, and arrays. Its use represents a guarantee by the programmer that within the scope of the pointer declaration the object pointed to can be accessed only by that pointer. Any violation of this guarantee renders the program undefined. This practice helps the compiler optimize certain sections of code because aliasing information can be more easily determined.

In the example that follows, the restrict keyword is used to tell the compiler that the function func1 is never called with the pointers a and b pointing to objects that overlap in memory. You are promising that accesses through a and b will never conflict; this means that a write through one pointer cannot affect a read from any other pointer. The precise semantics of the restrict keyword are described in the 1999 version of the ISO C standard.

Use of the restrict type qualifier with pointers

void func1(int * restrict a, int * restrict b)
{
/* func1's code here */
}

This example illustrates using the restrict keyword when passing arrays to a function. Here, the arrays c and d should not overlap, nor should c and d point to the same array.
Use of the restrict type qualifier with arrays

void func2(int c[restrict], int d[restrict])
{
int i;

for(i = 0; i < 64; i++)
{
c[i] += d[i];
d[i] += 1;
}
}Top

11 楼zcz0918（）回复于 2005-12-12 17:19:30 得分 0

C99不通用
至少偶没用过也没见过Top

12 楼piaozi2003（）回复于 2005-12-13 13:34:05 得分 0

OK!谢谢Top