keil C警告reference made to unresolved external

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keil C警告reference made to unresolved external
reference made to unresolved external
我在头文件中声明全局变量ACT,主函数定义初始化,用函数调用ACT的话就会出现这个警告应该如何解决
main.h
extern float ACT;
float ff(float ACT);
#include
void main()
{
float ACT=0.5,REF;
REF=ff(ACT);
}
float ff(float ACT)
{
return ACT;
}
函数大致类似于这样,

C语言中,不允许出现重名的全局变量和局部变量,改掉一个试试.
再问：不是全局变量需要先声明，然后再主函数初始化嘛？声明放在头文件中是不能初始化的
再答：是下面函数的形参 float ff(float ACT) 与全局变量 extern float ACT; 重名了。如果是一个全局变量，在后面的函数中可以不用做形参就直接使用。

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