cpp文件定义和使用中出现的multiple definition of报错

背景：

在一个A.cpp文件中定义了一些class和一些普通函数。在B.cpp文件中对A.cpp进行了include操作。报错：

tmp/ccyTkYe4.o: In function `TestDualLingualUpload()':/testUtil/TestDualLingualUpload.cpp:555: multiple definition of `TestDualLingualUpload()'/tmp/ccm9V4o9.o:/testUtil/TestDualLingualUpload.cpp:555: first defined here/tmp/ccyTkYe4.o: In function `TestDualLingualState(bool)':/testUtil/TestDualLingualUpload.cpp:591: multiple definition of `TestDualLingualState(bool)'/tmp/ccm9V4o9.o:/testUtil/TestDualLingualUpload.cpp:591: first defined here/tmp/ccyTkYe4.o: In function `TestDualLingualStateV2(unsigned char, bool)':/testUtil/TestDualLingualUpload.cpp:604: multiple definition of `TestDualLingualStateV2(unsigned char, bool)'/tmp/ccm9V4o9.o:/testUtil/TestDualLingualUpload.cpp:604: first defined here/tmp/ccyTkYe4.o: In function `TestHttpSearch()':/testUtil/TestDualLingualUpload.cpp:616: multiple definition of `TestHttpSearch()'/tmp/ccm9V4o9.o:/testUtil/TestDualLingualUpload.cpp:616: first defined here/tmp/ccyTkYe4.o: In function `TestDecodeUpload(char const*)':/testUtil/TestDualLingualUpload.cpp:634: multiple definition of `TestDecodeUpload(char const*)'/tmp/ccm9V4o9.o:/testUtil/TestDualLingualUpload.cpp:634: first defined here/tmp/ccyTkYe4.o: In function `TestDualLingualKrc()':/testUtil/TestDualLingualUpload.cpp:653: multiple definition of `TestDualLingualKrc()'/tmp/ccm9V4o9.o:/testUtil/TestDualLingualUpload.cpp:653: first defined here

分析：

这是由于编译是以cpp文件为单位的，所以会对A.cpp进行编译，而由于B.cpp中include了A.cpp所以在编译B.cpp的时候又再一次对A.cpp进行了一次编译，从而导致上述问题。其实解决方法也很简单，将A.cpp的以A.h或者A.hpp的方式存储即可。所以，按照通用的形式进行书写是可以避免很多坑的。