在 C 中我们可以拥有的指针的指针数量有多少限制？

Question

在 C 中，我知道我们可以用指针来做到这一点：

int *p;          /* an int pointer (ptr to an int) */
int **pp;        /* a pointer to an int pointer (ptr to a ptr to an int) */

甚至：

int **app[];            /* an array of pointers to int pointers */
int (**ppa)[];          /* a pointer to a pointer to an array of ints */
int (**ppf)();          /* a pointer to a pointer to a function returning an int */
int *(*pap)[];          /* a pointer to an array of int pointers */
int **fpp();            /* a function returning a pointer to an int pointer */

但是我们可以做一些像三分球无限的事情吗？例如：

int ***ppp;             /* a pointer to a pointer to an int pointer */
int ****pppp;           /* a pointer to a pointer to a pointer to an int pointer */

...以此类推直到无穷大。

我们可以拥有的指针的指针数量是否有上限？如果可以，上限是多少？

Answer 1

该标准没有规定任何上限。它所说的是编译器至少需要支持 12.

在实际代码中可以认为是无穷大。只有当你编写的程序编写的程序是任何人都不应该阅读的程序时，这才有意义。大多数程序员会说你应该拿三颗星作为警告。没有真正充分的理由，不要超过两个。

我在 gcc 上尝试了 10000，它成功了。我现在正在尝试使用 100000。一件有趣的事情是编译需要很长时间。编译花了几分钟，唯一的声明是一个指针声明，有 10000 个星。

生成C文件的代码：

// gen.c
#include <stdio.h>

int main()
{
    const size_t n = 10000;
    printf("int main(){int ");
    for(size_t i=0; i<n; i++)
        printf("*");
    printf("p;}\n");
}

运行:

$ gcc gen.c -c gen
$ ./gen > stars.c
$ gcc stars.c

回复评论：

这是一个有趣的实验，但我不会进一步研究它。

Answer 2

C 11 标准没有施加最大限制，实际上声明“实施应尽可能避免施加固定的转换限制。” in a footnote.

最小限制由 5.2.4 Environmental limits 给出：

The implementation shall be able to translate and execute at least one program that contains at least one instance of every one of the following limits:18)

127 nesting levels of blocks

63 nesting levels of conditional inclusion

12 pointer, array, and function declarators (in any combinations) modifying an arithmetic, structure, union, or void type in a declaration

63 nesting levels of parenthesized declarators within a full declarator

63 nesting levels of parenthesized expressions within a full expression

63 significant initial characters in an internal identifier or a macro name (each universal character name or extended source character is considered a single character)

31 significant initial characters in an external identifier (each universal character name specifying a short identifier of 0000FFFF or less is considered 6 characters, each universal character name specifying a short identifier of 00010000 or more is considered 10 characters, and each extended source character is considered the same number of characters as the corresponding universal character name, if any)

4095 external identifiers in one translation unit

511 identifiers with block scope declared in one block

4095 macro identifiers simultaneously defined in one preprocessing translation unit

127 parameters in one function definition

127 arguments in one function call

127 parameters in one macro definition

127 arguments in one macro invocation

4095 characters in a logical source line

4095 characters in a string literal (after concatenation)

65535 bytes in an object (in a hosted environment only)

15 nesting levels for #included files

1023 case labels for a switch statement (excluding those for any nested switch statements)

1023 members in a single structure or union

1023 enumeration constants in a single enumeration

63 levels of nested structure or union definitions in a single struct-declaration-list

符合标准的 C 编译器将提供至少 12 级指针间接寻址。

在 C 中我们可以拥有的指针的指针数量有多少限制？

What is the limit to the number of pointers to pointers we can have in C?

c

pointers

limit

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