make-07.html

unix make 文档

<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">ifdef foo</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">frobozz = yes</span></i></b></p>
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<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">else</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">frobozz = no</span></i></b></p>
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<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">endif</span></i></b></p>
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<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">&nbsp;</span></p>
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<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
例</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">1</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">中的结果是：“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">frobozz 
= yes</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”；而例</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">2</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">的结果是：“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">frobozz 
= no</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”。其原因就是在例</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">1</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">中，变量“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">foo</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”的定义是“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">foo 
= $(bar)</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”。虽然变量“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">bar</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”的值为空，但是“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifdef</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”判断的结果是真。因此当我们需要判断一个变量的值是否为空的情况时，需要使用“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifeq</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”（或者“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifneq</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”）而不是“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifdef</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”。可参考前两个小节的内容。</span></p>
<h3><a name="_gnu_make_7.2.4"><span lang="en-us">7</span><span lang="EN-US">.2.4<span style="font-style: normal; font-variant: normal; font-weight: normal; font-size: 7.0pt; font-family: Times New Roman">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</span></span><span style="font-family: 黑体">关键字“</span><span lang="EN-US">ifndef</span></a><span style="font-family: 黑体">”</span></h3>
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<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
关键字“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifndef</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”实现的功能和“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifdef</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”相反。格式为：</span></p>
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<b>
<span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: blue">
`ifdef VARIABLE-NAME'</span></b></p>
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<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
这个就不详细讨论了，它的功能就是实现了和“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifdef</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”相反的条件判断。</span></p>
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<span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">
&nbsp;</span></p>
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<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
在“</span><b><i><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial">CONDITIONAL-DIRECTIVE</span></i></b><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”这一行上，可以以若干个空格开始，</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">处理时会被忽略这些空格。但不能以</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">[Tab]</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">字符做为开始（不然就被认为是命令）。条件判断语句中，在除关键字（包括“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">endif</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”）之前、条件表达式参数中之外的其他任何地方都可以使用多个空格或</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">[Tab]</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">字符，它不会影响条件判断语句的功能。同样行尾也可以使用注释（“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">#</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”开始直到一行的结束）。“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">else</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”和“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">endif</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”也是条件判断语句的一部分。在书写时它们都是没有任何参数的，可以以多个空格开始（同样不能以</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">[Tab]</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">字符开始）多个空格或</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">[Tab]</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">字符结束。行尾同样可以有注释内容。</span></p>
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<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
在</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">读取</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">makefile</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">文件时计算表达式的值，并根据表达式的值决定判断语句中那一部分被作为此</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">Makefile</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">所要执行的内容（选择符合条件的语句）。因此在条件表达式中不能使用自动化变量，自动化变量在规则命令执行时才有效。更不能将一个完整的条件判断语句分写在两个不同的</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">makefile</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">文件中，在一个</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">makefile</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">文件使用指示符“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">include</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”包含另外一个</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">makefile</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">文件。</span></p>
<h2><a name="_gnu_make_7.3"><span style="font-size: 14pt" lang="en-us"><b>7</b></span><b><span lang="EN-US" style="font-size: 14.0pt">.3<span style="font-style: normal; font-variant: normal; font-weight: normal; font-size: 7.0pt; font-family: Times New Roman">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</span></span></b><span style="font-size: 14.0pt; font-family: 楷体_GB2312">
标记测试的条件语句</span></a></h2>

	<span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; color: #222222">
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	<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
	我们可以使用条件判断语句、变量“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">MAKEFLAGS</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”和函数“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">findstring</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”，实现对</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">命令行选项的测试。看一个例子：</span></p>
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<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">archive.a: ...</span></i></b></p>
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<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">ifneq (,$(findstring 
t,$(MAKEFLAGS)))</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 58.2pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">+touch 
archive.a</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 58.2pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">+ranlib -t 
archive.a</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">else</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 58.2pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">ranlib 
archive.a</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">endif</span></i></b></p>
<p class="MsoNormal" style="text-indent: 20.5pt">
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">&nbsp;</span></p>
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<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
这个条件语句判断</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">的命令行参数中是否包含“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-t</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”（用来更新目标文件的时间戳）。根据命令行参数情况完成对“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">archive.a</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”执行不同的操作。命令行前的“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">+</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”的意思是告诉</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">，即使</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">使用了“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-t</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”参数，“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">+</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”之后的命令都需要被执行。</span></p>
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