Can the C language define global variables in the header file?

Yes, but generally the definition of a global variable is not written in the header file.

Because if multiple C source files are added header files, it is easy to cause a redefinition problem. At this point the general compiler will prompt: "Multiple definition of ... first defined here" error.

The correct approach is to define a global variable in the C source file and add a declaration of that variable to the corresponding header file . For example:

　　//var.c 一个主要用于定义全局变量的c源文件 　　　　int g_a; 　　　　char g_x; 　　//var.h 用于声明定义的全局变量 　　　　extern int g_a; 　　　　extern char g_x;  　　//test.c 一个用于测试的头文件 　　　　#include <var.h> 　　　　void f() 　　　　{     　　 g_a = 1;     　　 g_x =  ‘x‘ ; 　　　　}

Can the C language define global variables in the header file?