在 Linux（和类 UNIX 系统）编程中，“open() ”和 “fopen() ”都用于打开文件，但它们有不同的用例、返回类型和行为。下面是两者的比较：

In Linux (and UNIX-like systems) programming, both `open()` and `fopen()` are used to open files, but they have different use cases, return types, and behaviors. Here's a comparison between the two:

`open()`

- 系统调用： `open()` 是一个低级系统调用。

- 头文件： 需要包含 `<fcntl.h>` 和 `<unistd.h>`。

- 返回类型： 返回一个文件描述符，它是一个用于与文件交互的简单整数。

- 缓冲： 不提供任何缓冲。输入/输出操作直接在文件上完成，这意味着它们是无缓冲的。

- 灵活性：允许对文件访问模式和标志（如非阻塞模式、直接 I/O 等）进行更精细的控制。

- 模式：`open()` 可以使用 `O_RDONLY`、`O_WRONLY`、`O_RDWR` 等标志以多种模式打开文件。

- 用例：非常适合底层文件操作、需要直接控制文件描述符或与操作系统级文件描述符交互时使用。

`open()`

- System Call: `open()` is a low-level system call.

- Header File: Requires the inclusion of `<fcntl.h>` and `<unistd.h>`.

- Return Type: Returns a file descriptor, which is a simple integer used to interact with the file.

- Buffering: Does not provide any buffering. Input/output operations are done directly on the file, which means they are unbuffered.

- Flexibility: Allows for finer control over file access modes and flags (e.g., non-blocking mode, direct I/O, etc.).

- Modes: `open()` can open files in a wide variety of modes using flags like `O_RDONLY`, `O_WRONLY`, `O_RDWR`, and more.

- Use Case: Ideal for low-level file operations and when you need direct control over the file descriptor or when you're interacting with OS-level file descriptors.

  

Example:

`fopen()`

- 标准库函数：`fopen()` 是 C 标准库的一部分（高级函数）。

- 头文件：要求包含 `<stdio.h>`。

- 返回类型： 返回一个 `FILE*` 指针，其他高级 I/O 函数（如 `fread()`、`fwrite()`、`fprintf()` 等）会使用该指针。

- 缓冲：为输入/输出操作提供缓冲，通过减少系统调用次数来提高性能。

- 灵活性： 虽然更容易使用，但与 `open()` 相比，`fopen()` 提供的直接控制较少。您通常会将它与 `“r”`、`“w”`、`“a”` 等简单模式一起使用。

- 模式： 支持读取、写入和追加的简单模式，使用的字符包括 `“r”`、`“w”`、`“a”`，以及可选的用于读/写的 `+`。

- 用例：适用于对简单性和可移植性要求较高的高级文件操作。

`fopen()`

- Standard Library Function: `fopen()` is part of the C standard library (higher-level function).

- Header File: Requires the inclusion of `<stdio.h>`.

- Return Type: Returns a `FILE*` pointer, which is used by other high-level I/O functions like `fread()`, `fwrite()`, `fprintf()`, etc.

- Buffering: Provides buffering for input/output operations, which improves performance by minimizing the number of system calls.

- Flexibility: While easier to use, `fopen()` offers less direct control compared to `open()`. You typically use it with simple modes like `"r"`, `"w"`, `"a"`, etc.

- Modes: Supports simple modes for reading, writing, and appending, using characters like `"r"`, `"w"`, `"a"`, with optional `+` for read/write.

- Use Case: Ideal for high-level file operations where simplicity and portability are important.

Example:

Summary of Differences:

- open()`： 低级，无缓冲，返回文件描述符，提供更多控制。

- `fopen()`： 高级，有缓冲，返回一个 `FILE*`，在大多数 I/O 操作中使用更简单。

如果直接处理系统级文件描述符或需要精细控制，则应使用 `open()`。对于性能和易用性都很重要的高级文件 I/O 任务，`fopen()` 是更好的选择。

- `open()`: Low-level, unbuffered, returns a file descriptor, provides more control.

- `fopen()`: High-level, buffered, returns a `FILE*`, simpler to use for most I/O operations.

If you're working directly with system-level file descriptors or need fine-grained control, you’d use `open()`. For higher-level file I/O tasks where performance and ease of use are important, `fopen()` is the better choice.