什么是用C这种风格的语法？ [英] What is this style of syntax in C?

问题描述

通过 sys.c 线123：

 的void * sys_call_table的[__ NR_syscalls] =
{
    [0 ... __NR_syscalls-1] = sys_ni_syscall，
＃包括LT＆; ASM / unistd.h中＆GT;
};
 

sys_call_table的是一个通用的指针数组，我可以看到。然而什么是符号：

  [0 ... __NR_syscalls-1]
 

什么是 ... ？

---

编辑：结果
我在这里学会了另一种C招：的#include＆LT; ASM / unistd.h中＆GT; 将 preprocessed 的并与其内容替换，并且分配到 [0 ... _NR_syscalls-1] 。

解决方案

这是使用初始化 指定初始化 。

范围根据初始化一个GNU GCC扩展。

  

要初始化一个范围的元素为相同的值，写 [第一...最后] =值。这是一个GNU扩展。例如，

  INT宽度[] = {[0 ... 9] = 1，[10 ... 99] = 2，[100] = 3};
 

这是不可移植。与 -pedantic 有这么告诉你编译。

它是如何在这里工作？结果
在preprocessor替换的#include＆LT; ASM / unistd.h中＆GT; ，其实际内容（的它定义杂项符号常量和类型，并声明辅助功能< /在基于范围构建体，然后将其进一步用于初始化指针数组青霉>）。

From sys.c line 123:

void *sys_call_table[__NR_syscalls] = 
{
    [0 ... __NR_syscalls-1] = sys_ni_syscall,
#include <asm/unistd.h>
};

sys_call_table is a generic pointer to arrays, I can see that. However what is the notation:

[0 ... __NR_syscalls-1]

What is the ...?

---

EDIT:
I learned another C trick here: #include <asm/unistd.h> will be preprocessed and replaced with its content and assigned to [0 ... _NR_syscalls-1].

解决方案

It is initialization using Designated Initializers.

The range based initialization is a gnu gcc extension.

To initialize a range of elements to the same value, write [first ... last] = value. This is a GNU extension. For example,

 int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };

It is not portable. Compiling with -pedantic with tell you so.

How does it work here?
The preprocessor replaces #include <asm/unistd.h> with its actual contents(it defines miscellaneous symbolic constants and types, and declares miscellaneous functions) in the range based construct, which are then further used for initializing the array of pointers.

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