限制数组大小的目的是什么？

Question

我明白restrict是什么意思，但是我对这样的usage/syntax有点困惑：

#include <stdio.h>

char* foo(char s[restrict], int n)
{
        printf("%s %d\n", s, n);
        return NULL;
}

int main(void)
{
        char *str = "hello foo";
        foo(str, 1);

        return 0;
}

编译成功 gcc main.c -Wall -Wextra -Werror -pedantic

限制在这种情况下如何工作并由编译器解释？

gcc 版本：5.4.0

Answer 1

来自restrict type qualifier

In a function declaration, the keyword restrict may appear inside the square brackets that are used to declare an array type of a function parameter. It qualifies the pointer type to which the array type is transformed:

和示例：

void f(int m, int n, float a[restrict m][n], float b[restrict m][n]);

Answer 2

首先，

  char* foo(char s[restrict], int n) { ....

与

相同

  char* foo(char * restrict s, int n) {...

C11 章节 §6.7.6.2

允许语法

[...] The optional type qualifiers and the keyword static shall appear only in a declaration of a function parameter with an array type, and then only in the outermost array type derivation.

这里restricted的目的是提示编译器对于函数的每次调用，实际参数仅通过指针[=15]访问=].

限制数组大小的目的是什么？

What is the purpose of restrict as size of array?

c

gcc

restrict-qualifier