我可以获取"FILE *"的访问方式吗? [英] Can I get the access mode of a `FILE*`?

问题描述

我必须在Mac OS X上的C语言中复制一个 FILE * (不幸的是，毫无疑问，一直使用POSIX int 文件描述符)，所以我提出了具有以下功能:

I have to duplicate a FILE* in C on Mac OS X (using POSIX int file descriptors all the way is unfortunately out of question), so I came up with the following function:

static FILE* fdup(FILE* fp, const char* mode)
{
    int fd = fileno(fp);
    int duplicated = dup(fd);
    return fdopen(duplicated, mode);
}

它工作得很好，除了它有一个丑陋的小部分，我再次要求文件模式，因为 fdopen 显然无法确定它本身.

It works very well, except it has that small ugly part where I ask for the file mode again, because fdopen apparently can't determine it itself.

此问题并不严重，因为基本上，我只是将其用于 stdin ， stdout 和 stderr (显然，我了解这三种方式的访问方式).但是，如果我自己不知道的话，它会更优雅.这可能是可能的，因为 dup 调用不需要它.

This issue isn't critical, since basically, I'm just using it for stdin, stdout and stderr (and obviously I know the access modes of those three). However, it would be more elegant if I didn't have to know it myself; and this is probably possible since the dup call doesn't need it.

如何确定 FILE * 流的访问模式?

How can I determine the access mode of a FILE* stream?

推荐答案

您不能，但是您可以确定基础文件描述符的模式:

You can't, but you can determine the mode for the underlying file descriptor:

int fd = fileno(f);
int accmode = fcntl(fd, F_GETFL) & O_ACCMODE;

然后您可以根据 accmode 是 O_RDONLY ， O_WRONLY 选择合适的模式传递给 fdopen 或 O_RDWR .

You can then choose an appropriate mode to pass to fdopen based on whether accmode is O_RDONLY, O_WRONLY, or O_RDWR.

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