如何为m4宏文件包含的ifdef保护？

Question

对于C头文件，可以防止多次包含头文件，例如：

#ifndef MY_FOO_H
#define MY_FOO_H

[...]

#endif

如何在m4中做同样的事情，include()以便对同一文件的多个宏调用只会导致内容被包含一次？

具体来说，我想做一个涉及使用宏的ifdef保护changequote（我不会用dnls使我的代码混乱）：

最初，当我执行以下操作时，多个包含仍会破坏引号：

更改quote_file.m4：

ifdef(my_foo_m4,,define(my_foo_m4,1)
changequote([,])
)

更改quote_invocation.m4：

include(changequote_file.m4)
After first include invocation:
[I should not have brackets around me]
`I should have normal m4 quotes around me'
include(changequote_file.m4)
After second include invocation:
[I should not have brackets around me]
`I should have normal m4 quotes around me'

调用m4 changequote_invocation.m4收益率：

After first include invocation:
I should not have brackets around me
`I should have normal m4 quotes around me'


After second include invocation:
[I should not have brackets around me]
`I should have normal m4 quotes around me'

Answer 1

最直接的方法是对该cpp版本进行几乎字面上的翻译：

ifdef(`my_foo_m4',,`define(`my_foo_m4',1)dnl
(rest of file here)
')dnl

因此，如果my_foo_m4已定义，则文件将扩展为空，否则将评估其内容。