C++编译出现 类型未声明

Question

C++ 头文件中已经用#include 包含了类型声明的头文件，为什么还会提示该类型没有声明（error: 'cfdemCloudIB' has not been declared）？已经排除了类之间互相包含的可能性；还有其他可能情况吗？

Answer 1

1. Are you compiling under linux or window?

2. If you are compiling under Linux, did you forget to add the path of the header file you included under the -I option? The compilation principle under window is similar.

Answer 2

The order in which header files are included will also have an impact.

Give me a chestnut
a.h

#ifndef INT
define INT32 int
#endif

b.h

#define INT long

m.c

#include "b.h"
#include "a.h"

INT32 x = 0;    // 这里将报错，因为INT32实际上是没有定义的

For the above code, the two header files contain familiar ones and can be reversed.