错误

不允许类内初始化，非常量静态成员；

class.cpp:7:13: error: ISO C++ forbids in-class initialization of non-const static member ‘A::b’static int b=0;

代码

class A
{virtual void fun1(){};int a;
public:static int b=0;

为什么要加这么个限制

如果包含这个类的头文件，被多个cpp文件引用，可能造成困扰。
https://stackoverflow.com/questions/9656941/why-cant-i-initialize-non-const-static-member-or-static-array-in-class?noredirect=1&lq=1
https://www.stroustrup.com/bs_faq2.html#in-class
The Design and Evolution of C++

So why do these inconvenient restrictions exist? A class is typically declared in a header file and a header file is typically included into many translation units. However, to avoid complicated linker rules, C++ requires that every object has a unique definition. That rule would be broken if C++ allowed in-class definition of entities that needed to be stored in memory as objects. See D&E for an explanation of C++'s design tradeoffs.

但是为了适应需求：在c++17里，有了这种语法：static inline int maxNumberOfNeighbors = 4;
如果使用c++11 编译，出现warning：

class.cpp:7:20: warning: inline variables are only available with -std=c++17 or -std=gnu++17static inline int b=0;

使用c++17，编译正常。

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C++：错误：ISO C++ forbids in-class initialization of non-const static member ‘A::b’

错误

代码

为什么要加这么个限制

C++：错误：ISO C++ forbids in-class initialization of non-const static member ‘A::b’相关推荐

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