C中打开文件功能中的标志和模式之间的关系是什么 [英] What's the connection between flags and mode in open file function in C

问题描述

我是C语言的初学者，对C语言中打开文件功能中的标志和模式参数有疑问 所以C的open函数是:

I'm a beginner in C, have a question about the flags and mode paramaters in open file function in C so C's open function is :

int open(char *filename, int flags, mode_t mode);

和标志的一些宏是:

• O_RDONLY:只读
• O_WRONLY:仅写
• O_RDWR:读写

• O_RDONLY: Reading only
• O_WRONLY: Writing only
• O_RDWR: Reading and writing

和模式位类似:

我不明白的是， 假设我们有一个开放功能，如:

What I don't understand is, let say we have a open function as:

fd = Open("foo.txt", O_RDONLY, S_IWOTH);

所以O_RDONLY指定我们只能读取文件，但是S_IWOTH指定任何人都可以写入该文件，这不是彼此矛盾吗?

so O_RDONLY specifies that we can only read the file, but S_IWOTH specifies that anyone can write this file, isn't that they contradict to each other?

推荐答案

标志决定此时在打开此文件的过程中要应用的属性(让我们调用这就是会话")-这会影响文件打开时的处理方式(或更正确地说，是文件描述符的处理方式).

The flags decide the properties to be applied during opening of this file at this time (let's call this the "session") - this affects what you can do with the file while it's open (or, more correctly, what you can do with the file descriptor).

模式决定在打开过程中创建文件的属性-这会影响以后任何人打开文件的方式.

The mode decide the properties of the file should it be created as part of the opening process - this affects how anyone can open the file in future.

您的特定示例(尽管使用正确的open而不是Open):

Your specific example (albeit with the correct open rather than Open):

fd = open("foo.txt", O_RDONLY, S_IWOTH);

并不是真正相关的，因为不会在没有O_CREAT标志^(a)的情况下创建文件 .

is not really relevant since the file won't be created without the O_CREAT flag^(a).

但是，如果您提供了O_CREAT，则完全可以接受创建文件，该文件允许任何人对其进行写操作，但是要以只读模式在此会话中打开该文件.

However, had you supplied O_CREAT, it's perfectly acceptable to create the file allowing anyone to write to it, but have it opened for this session in read-only mode.

^(a)某些系统具有 other 标志，这些标志在某些情况下可能会创建文件.例如，Linux具有O_TMPFILE标志.

^(a) Some systems have other flags which may create the file under some circumstances. For example, Linux has the O_TMPFILE flag.

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