Скачать или смотреть How to Read Directories in C Without Using readdir

Learn how to navigate directories in C programming without using `readdir` and discover why it may be limited by the system calls available.
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Navigating Directory Structures in C: Beyond readdir

When delving into the world of C programming, especially under the POSIX environment on Linux, many developers encounter the need to read directory contents. The typical way to retrieve the names of files and subdirectories involves the use of readdir() and opendir() functions provided by the <dirent.h> library. However, some programmers feel the need to access directories through lower-level system calls like open() and read(). This raises an important question: Can we read a directory using open() and read() instead of readdir()?

The Simple Answer: No

To put it straightforwardly, the answer is no. The functions open() and read() are designed to operate on files, while opendir() and readdir() specifically work with directory streams. Here’s a breakdown of the two pairs of functions and how they differ:

Understanding the Functionality

File Operations: open() and read()

open(const char *pathname, int flags) is used to open files.

read(int fd, void *buf, size_t count) reads data from the file descriptor fd into a buffer.

Directory Operations: opendir() and readdir()

opendir(const char *name) opens a directory stream corresponding to the directory name and returns a pointer to the directory stream.

readdir(DIR *dirp) reads the next entry from the directory stream dirp, returning a pointer to a dirent structure, which contains the name of the file or subdirectory.

Why the Distinction Matters

Data Structures: The system treats directories and files differently. Directories are not merely files; they store information about contained files and folders in a specific data structure.

System Calls: Using open() and read() does not give you structured access to the entries in a directory and would usually lead to undesired results or require complex processing that readdir() handles efficiently.

Conclusion: Stick to readdir() and opendir()

Given these distinctions, it's highly advisable to use the correct set of functions when interacting with directories. While it may seem tempting to use open() and read(), attempting this approach can lead to unnecessary complications and inefficient coding practices.

If you are keen on exploring directories in pure C while maintaining system compliance and efficiency, opt for readdir(). Not only does this significantly ease your task, but it also aligns with best practices in programming for working within a POSIX environment.

This knowledge will not only make your coding journey more straightforward but will also enhance your understanding of how the operating system manages files and directories.

Continue learning, and happy coding!