我怎么能在参数选择SCANDIR功能 [英] how can I parameterize select function in scandir

问题描述

该SCANDIR（）函数扫描目录dir，呼吁
选择（）上的每个目录项为INT（*过滤器）（常量结构的dirent *）
在过滤器中使用如何传递模式值作为参数的fnmatch（为const char *模式，为const char *字符串，整数标志）的功能？

The scandir() function scans the directory dir, calling select() on each directory entry as "int(*filter)(const struct dirent *)" How can I pass pattern value as parameter to fnmatch(const char *pattern, const char *string, int flags) function used in filter ?

下面我的示例code

Here my sample code

int my_selectgrf(const struct dirent *namelist)
{
   int  r = 0;
   char     my_pattern[] = "*.grf";
   r = fnmatch(my_pattern, namelist->d_name, FNM_PERIOD);

   return (r==0)?1:0;
}
scandir("/pub/data/grf", &namelist, my_selectgrf, alphasort);

我的目标是能够使用my_pattern作为输入参数。

my goal is to be able to use my_pattern as input parameter.

推荐答案

答案很简单：你不能。这是一个残暴恶劣的API，它是彻底的可耻这样的事情被添加到POSIX最近在2008年（基于glibc的一个不好的设计）。这种API的没有办法参数，或通过它的上下文应该已经超过20年前废除了。

The short answer: You can't. This is an atrociously bad API, and it's outright shameful that something like this was added to POSIX as recently as 2008 (based on a bad design in glibc). This kind of API without a way to parameterize it or pass it a context should have been abolished 20+ years ago.

随着中说，有一些解决方法：

With that said, there are some workarounds:

方法1：使用全局变量，如果你的code需要是线程安全的，确保只有一个线程可以使用 SCANDIR 与给定同时扫描功能，通过锁定。这当然的连载的使用情况，如果你真的想被调用多个线程，其功能可能是不能接受的。

Approach 1: Use a global variable, and if your code needs to be thread-safe, ensure that only one thread can be using scandir with the given scan function at a time, by locking. This of course serializes usage, which is probably not acceptable if you actually want to be calling the function from multiple threads.

方法二：使用线程本地存储，无论是海湾合作委员会 __线程关键字（或C11 _Thread_local 关键字，这GCC可悲的是仍然不接受）或POSIX pthread_setspecific 和家人。这还算干净，但不幸的是它可能不正确;如果 SCANDIR 实施内部使用多线程，则参数可能无法在一些调用可用回扫描功能。在present，我不相信也有 SCANDIR 多线程的实现。

Approach 2: Use thread-local storage, either the GCC __thread keyword (or the C11 _Thread_local keyword, which GCC sadly still does not accept) or POSIX pthread_setspecific and family. This is fairly clean, but unfortunately it may not be correct; if the implementation of scandir internally used multiple threads, the parameter could fail to be available in some calls back to the scan function. At present, I don't believe there are multi-threaded implementations of scandir.

现在，更好的解决办法：

Now, the better solution:

沟 SCANDIR ，写自己的函数做同样的事情，用正确的API。这是只有几行呢。

Ditch scandir and write your own function to do the same thing, with the proper API. It's only a few lines anyway.

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