c - 使用 char *、unsigned char * 和 signed char * 别名

Question

char *(和限定的变体)可以为任何东西起别名。 是 signed char * 和 unsigned char *(及其限定变体) 免于此？

换句话说，如果我不希望它们作为其他指针参数的别名，我了解到将 restrict 应用于 char* 函数参数是个好主意类型(因为它们可以给它们起别名):

int func(struct foo *f, char * restrict s /*different object*/);

我可以像这样为有符号和无符号字符变体删除 restrict 关键字吗？

int sfunc(struct foo *f, signed char *s /*different object*/);
int ufunc(struct foo *f, unsigned char *s /*different object*/);

也可以指向相同类型的有符号和无符号变体 互为别名？换句话说，如果我期望一个指向 int 的指针和一个指向 unsigned 的指针，并且它们应该指向不同的对象，那么 int * 和 unsigned * 参数都应该是 restrict-限定？

/* i and u should be different */
int uifunc(int * /*restrict?*/ i, unsigned * /*restrict?*/ u); 

Answer 1

规则是 (C11 6.5/7):

An object shall have its stored value accessed only by an lvalue expression that has one of the following types:

• a type compatible with the effective type of the object,
• a qualified version of a type compatible with the effective type of the object,
• a type that is the signed or unsigned type corresponding to the effective type of the object,
• a type that is the signed or unsigned type corresponding to a qualified version of the effective type of the object,
• an aggregate or union type that includes one of the aforementioned types among its members (including, recursively, a member of a subaggregate or contained union), or
• a character type.

char、signed char 和unsigned char 都是字符类型 (ref: 6.2.5/15)。前面的项目符号还回答了您关于有符号和无符号类型的问题。

请记住，固定宽度类型是 typedef，它可能引用各种其他类型，所以要小心。