g++多文件编译和简单MakeFile文件写法

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g++多文件编译和简单MakeFile文件写法

分类： linux相关知识2013-12-02
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上文(g++基本用法)介绍简单的g++编译器的用法，只是针对没有依赖关系的单个文件的操作，当我们有多个文件需要编译的时候，是如何工作的呢？下面以简单的实例进行介绍，然后把实例以MakeFile文件实现，并对MakeFile文件进行简单介绍。

准备工作，下面是需要的简单实例文件及代码:
main.cxx

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ cat main.cxx</span>
<span style="font-family: 'Courier New', monospace;">#include <iostream></span>
<span style="font-family: 'Courier New', monospace;">#include "printf1.hxx"</span>
<span style="font-family: 'Courier New', monospace;">#include "printf2.hxx"</span>
<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ g++ -c main.cxx</span>

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ g++ -c  printf1.cxx</span>

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ g++ -c printf2.cxx</span>
<span style="font-family: 'Courier New', monospace;">
int main(){ printf1(); printf2();}</span>
<span style="font-family: 'Courier New', monospace;">printf1.hxx</span>
<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ cat printf1.hxx</span>
<span style="font-family: 'Courier New', monospace;">#ifndef _PRINTF_1_H_</span>
<span style="font-family: 'Courier New', monospace;">#define _PRINTF_1_H_</span>

<span style="font-family: 'Courier New', monospace;">void printf1();</span>

<span style="font-family: 'Courier New', monospace;">#endif</span>
<span style="font-family: 'Courier New', monospace;">printf1.cxx</span>
<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ cat printf1.cxx</span>
<span style="font-family: 'Courier New', monospace;">#include "printf1.hxx"</span>
<span style="font-family: 'Courier New', monospace;">#include <iostream></span>

<span style="font-family: 'Courier New', monospace;">using namespace std;</span>

<span style="font-family: 'Courier New', monospace;">void printf1()</span>
<span style="font-family: 'Courier New', monospace;">{</span>
<span style="font-family: 'Courier New', monospace;">        cout<<"printf1"<<endl;</span>
<span style="font-family: 'Courier New', monospace;">}</span>
<span style="font-family: 'Courier New', monospace;">printf2.hxx</span>
<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ cat printf2.hxx</span>
<span style="font-family: 'Courier New', monospace;">#ifndef _PRINTF_2_H_</span>
<span style="font-family: 'Courier New', monospace;">#define _PRINTF_2_H_</span>

<span style="font-family: 'Courier New', monospace;">void printf2();</span>

<span style="font-family: 'Courier New', monospace;">#endif</span>
<span style="font-family: 'Courier New', monospace;">printf2.cxx</span>
<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ cat printf2.cxx</span>
<span style="font-family: 'Courier New', monospace;">#include "printf2.hxx"</span>
<span style="font-family: 'Courier New', monospace;">#include <iostream></span>

<span style="font-family: 'Courier New', monospace;">using namespace std;</span>

<span style="font-family: 'Courier New', monospace;">void printf2()</span>
<span style="font-family: 'Courier New', monospace;">{</span>
<span style="font-family: 'Courier New', monospace;">        cout<<"printf2"<<endl;</span>
<span style="font-family: 'Courier New', monospace;">}</span>
共计<span style="font-family: 'Courier New', monospace;">5</span>个文件，<span style="font-family: 'Courier New', monospace;">3</span>个<span style="font-family: 'Courier New', monospace;">cxx</span>文件，<span style="font-family: 'Courier New', monospace;">2</span>个<span style="font-family: 'Courier New', monospace;">hxx</span>头文件

1、手动多文件编译
①先分别直接汇编（编译）为.o文件

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ g++ -c main.cxx</span>

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ g++ -c printf1.cxx</span>

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ g++ -c printf2.cxx</span>

②链接阶段

如果直接执行

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ g++ main.cxx -o main</span>
<span style="font-family: 'Courier New', monospace;">/tmp/cc9LFDvP.o:main.cxx:(.text+0xc): undefined reference to `printf1()'</span>
<span style="font-family: 'Courier New', monospace;">/tmp/cc9LFDvP.o:main.cxx:(.text+0x11): undefined reference to `printf2()'</span>
<span style="font-family: 'Courier New', monospace;">collect2: ld </span>返回<span style="font-family: 'Courier New', monospace;"> 1</span>
出现上边错误，原因是编译器找不到<span style="font-family: 'Courier New', monospace;">printf1()</span>和<span style="font-family: 'Courier New', monospace;">printf2()</span>的定义。

所以需要将3个obj文件链接到一个文件上：

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ g++ main.cxx printf1.cxx printf2.cxx -o main</span>

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ ./main</span>
<span style="font-family: 'Courier New', monospace;">printf1</span>
<span style="font-family: 'Courier New', monospace;">printf2</span>
并输出结果。

这样就能解决多文件编译问题，但是一般情况下，一个项目下的文件比较多，如果这样输入，比较费劲，所以就需要把编译过程写进一个MakeFile文件中

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ cat makefile</span>
<span style="font-family: 'Courier New', monospace;">cc=g++</span>
<span style="font-family: 'Courier New', monospace;">exe=main</span>
<span style="font-family: 'Courier New', monospace;">obj=main.o printf1.o printf2.o</span>

<span style="font-family: 'Courier New', monospace;">$(exe):$(obj)</span>
<span style="font-family: 'Courier New', monospace;">        $(cc) -o $(exe) $(obj)</span>
<span style="font-family: 'Courier New', monospace;">main.o:main.cxx</span>
<span style="font-family: 'Courier New', monospace;">        $(cc) -c main.cxx</span>
<span style="font-family: 'Courier New', monospace;">printf1.o:printf1.cxx</span>
<span style="font-family: 'Courier New', monospace;">        $(cc) -c printf1.cxx</span>
<span style="font-family: 'Courier New', monospace;">printf2.o:printf2.cxx</span>
<span style="font-family: 'Courier New', monospace;">        $(cc) -c printf2.cxx</span>
<span style="font-family: 'Courier New', monospace;">clean:</span>
<span style="font-family: 'Courier New', monospace;">        rm -rf *.o main</span>
其中
<span style="font-family: 'Courier New', monospace;">cc=g++</span>
<span style="font-family: 'Courier New', monospace;">exe=main</span>
<span style="font-family: 'Courier New', monospace;">obj=main.o printf1.o printf2.o</span>
为变量的定义，<span style="font-family: 'Courier New', monospace;">$(...)</span>作为引用，可以分析一下，是不是和上文中单个操作效果一样？

执行过程：

<span style="font-family: 'Courier New', monospace;">Administrator@72cec870236147e /home/liujl/mytest</span>
<span style="font-family: 'Courier New', monospace;">$ make</span>
<span style="font-family: 'Courier New', monospace;">g++ -c main.cxx</span>
<span style="font-family: 'Courier New', monospace;">g++ -c printf1.cxx</span>
<span style="font-family: 'Courier New', monospace;">g++ -c printf2.cxx</span>
<span style="font-family: 'Courier New', monospace;">g++ -o main main.o printf1.o printf2.o</span>

makefile可以参考：
1、ASimple
Makefile Tutorial
2、中文makefile教程

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