autoconf AS_IF没有执行正确的分支 [英] autoconf AS_IF doesn't execute correct branch

问题描述

在autoconf脚本中，尤其是在 AS_IF 中，我有点神秘.

I'm having a bit of a mystery in a autoconf script, specifically AS_IF.

以下是相关代码:

AC_CHECK_FUNCS([eventfd], [AC_DEFINE([NN_HAVE_EVENTFD])])
AC_CHECK_FUNCS([pipe], [AC_DEFINE([NN_HAVE_PIPE])])
AC_CHECK_FUNCS([pipe2], [
    AC_DEFINE([NN_HAVE_PIPE2])
    CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
])
AC_SEARCH_LIBS([socketpair], [], [AC_DEFINE([NN_HAVE_SOCKETPAIR])])

即检查它们的存在.它们可以正常工作并定义正确的符号.在这种情况下，仅定义了 NN_HAVE_PIPE 和 NN_HAVE_SOCKETPAIR ，这是正确的，因为这是HP-UX系统.

i.e. checking for their existance. These work correctly and define the correct symbols. In this case, only NN_HAVE_PIPE and NN_HAVE_SOCKETPAIR gets defined, which is correct as this is a HP-UX system.

现在到神秘的部分.稍后在configure.ac中，有条件地引用这些符号:

Now to the mystery part. Later in the configure.ac, there's a conditional referring to these symbols:

echo "ac_cv_func_eventfd: $ac_cv_func_eventfd"
AS_IF([test x"$ac_cv_func_eventfd"=xyes], [
    AC_DEFINE([NN_USE_EVENTFD])], [
    AS_IF([test x"$ac_cv_func_pipe"=xyes], [
        AC_DEFINE([NN_USE_PIPE])], [
        AS_IF([test x"$ac_cv_func_socketpair"=xyes], [
            AC_DEFINE([NN_USE_SOCKETPAIR])], [
            AC_MSG_ERROR([No signaling supported])
        ])
    ])
])

即使 ac_cv_func_eventfd 的值是 no (我添加了回显行以确保)，还是定义了 NN_USE_EVENTFD ！

Even though ac_cv_func_eventfd has value no (I added the echo line to make sure), NN_USE_EVENTFD gets defined anyway!

由于 AS_IF 宏的定义如下:

AS_IF (test1, [run-if-true1], ..., [run-if-false])

对我来说，代码似乎很正确，不是吗?有没有人可以阐明这种行为?

To me, the code seems quite correct, no? Is there anyone that can shed some light on this behavior?

Autoconf版本为2.67.操作系统是HP-UX 11.31 ia64.

Autoconf version is 2.67. The OS is HP-UX 11.31 ia64.

推荐答案

不太正确.您必须从以下位置修复 AS_IF 测试:

Not quite correct. You must fix your AS_IF test from:

test x"$ac_cv_func_eventfd"=xyes

到

 test x"$ac_cv_func_eventfd" = xyes

请注意在 = 周围插入空格.其他 AS_IF s中的其他测试也是如此.

Note the insertion of spaces around the =. Same goes for the other tests in the other AS_IFs.

要验证这一点，您可以尝试在命令行上看到它:

To verify this you can try seeing this at the command line:

if test x"no"=xyes; then echo "yes"; else echo "no"; fi

vs.

if test x"no" = xyes; then echo "yes"; else echo "no"; fi

这篇关于autoconf AS_IF没有执行正确的分支的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！