posix - 如果 _POSIX_VDISABLE 值为 -1 会怎样？

Question

在POSIX _POSIX_VDISABLE 值中如果为-1，则所有终端设备文件的特殊字符都没有禁用字符；否则该值是禁用字符值..

可以请任何人帮助我理解这一点。我无法理解这个的确切含义。

请

Answer 1

如果您查看 definition of special characters ，那应该意味着(thre '-1' 值)，所有这些特殊字符都处于事件状态:

In canonical input, the terminal driver recognizes a number of special characters which perform various control functions.
These include the ERASE character (usually DEL) for editing input, and other editing characters.
The INTR character (normally Ctrl-c) for sending a SIGINT signal, and other signal-raising characters, may be available in either canonical or noncanonical input mode.

你有很多这样的特殊角色:

Characters for Input Editing

BSD Extensions to Editing Characters

Characters that Cause Signals

Special Characters for Flow Control

Other Special Characters

已经提出了一个问题，看看 such a value was portable (确实总是编译)是否在 1997 年:

The wording in section 2.9.4:

If any of the constants in Table 2-11 are defined to have value -1 in the header ....

can suggest, on casual reading, code like the following to minimize size and optimize efficiency for each implementation:

#ifdef _POSIX_VDISABLE
#if    _POSIX_VDISABLE == -1
    /* code that assumes no vdisable capability */
#else
    /* code that assumes vdisable capability */
#endif
#else
    /* code that uses pathconf() to determine vdisable capability */
#endif

interpretation #34 表明它会。

By using these values at COMPILE-TIME, a portable POSIX.1 application can avoid loading all pathconf() related code associated with a symbol in Table 2-11 when the symbol is defined.