能否在头文件中定义全局static变量？
一、在没有类定义的头文件中定义全局static变量g_static。
用gcc和g++都可以编译。但运行结果显示，在test.c和main.c中，变量的值相同，但地址不同，说明是两个变量。
frank@userver:~/project/test/static-test/static1_c$ cat static.h
#ifndef STATIC_H
#define STATIC_H
static int g_static = 56;
#endif // #ifndef STATIC_H
frank@userver:~/project/test/static-test/static1_c$ cat test.h
#ifndef TEST_H
#define TEST_H
void test();
#endif // #ifndef TEST_H
frank@userver:~/project/test/static-test/static1_c$ cat test.c
#include <stdio.h>
#include "static.h"
#include "test.h"
void test(){
printf("[%s] g_static(%p,%u)\n", __FILE__, &g_static, g_static);
}
frank@userver:~/project/test/static-test/static1_c$ cat main.c
#include <stdio.h>
#include "static.h"
#include "test.h"
int main(){
printf("[%s] g_static(%p,%u)\n", __FILE__, &g_static, g_static);
test();
return 0;
}
frank@userver:~/project/test/static-test/static1_c$ g++ main.c test.c
frank@userver:~/project/test/static-test/static1_c$ ./a.out
[main.c] g_static(0x601040,56)
[test.c] g_static(0x601044,56)
frank@userver:~/project/test/static-test/static1_c$ gcc main.c test.c
frank@userver:~/project/test/static-test/static1_c$ ./a.out
[main.c] g_static(0x601040,56)
[test.c] g_static(0x601044,56)
二、在有类定义的头文件中定义全局static变量。
用g++可以编译。
在类的成员函数中，g_static的地址保持一致，说明在类的不同的对象中会访问到同一个全局static变量。
在类外部的函数中，运行结果与编译顺序有关。
在先编译的文件的函数中，g_static地址与类的成员函数一致，说明与类内部的g_static是同一个变量。。
但是在后编译的文件的函数中，g_static的地址不同，说明是另一个变量。
frank@userver:~/project/test/static-test/static1_cpp$ cat static.h
#ifndef STATIC_H
#define STATIC_H
#include<iostream>
using std::cout;
using std::endl;
static int g_static = 10;
class TestType{
public:
TestType(){}
void Show()const{
cout << "this=" << this << ", ";
cout << "g_static:(" << &g_static << ", " << g_static << ")\n";
}
};
#endif // #ifndef STATIC_H
frank@userver:~/project/test/static-test/static1_cpp$ cat test.h
#ifndef TEST_H
#define TEST_H
void test();
#endif // #ifndef TEST_H
frank@userver:~/project/test/static-test/static1_cpp$ cat test.cpp
#include "test.h"
#include "static.h"
void test(){
cout << __func__ << endl;
cout << "g_static = (" << &g_static << ", " << g_static << ")\n";
TestType obj;
obj.Show();
}
frank@userver:~/project/test/static-test/static1_cpp$ cat main.cpp
#include "test.h"
#include "static.h"
int main(){
cout << __func__ << endl;
cout << "g_static: (" << &g_static << ", " << g_static << ")\n";
TestType obj;
obj.Show();
test();
}
frank@userver:~/project/test/static-test/static1_cpp$ g++ main.cpp test.cpp
frank@userver:~/project/test/static-test/static1_cpp$ ./a.out
main
g_static: (0x602078, 10)
this=0x7fff09eba08f, g_static:(0x602078, 10)
test
g_static = (0x60207c, 10)
this=0x7fff09eba05f, g_static:(0x602078, 10)
frank@userver:~/project/test/static-test/static1_cpp$ g++ test.cpp main.cpp
frank@userver:~/project/test/static-test/static1_cpp$ ./a.out
main
g_static: (0x60207c, 10)
this=0x7fffdad480ef, g_static:(0x602078, 10)
test
g_static = (0x602078, 10)
this=0x7fffdad480bf, g_static:(0x602078, 10)
frank@userver:~/project/test/static-test/static1_cpp$
三、结论：不要在头文件中定义全局static变量。
