有没有办法访问 main.c 中定义的静态全局变量并在另一个文件中修改它？

Question

For example:

In main.c

static glob_var;

I want to modify the value of glob_var in another file say file1.c

Answer 1

Making an variable static makes its identifier inaccessible from other translation unit (what usually means other C-file). You can either

1. Make the variable non-static.

//main.c

int glob_var;


//file1.c

extern int glob_var;

Note that the declaration should be put to a header file.

2. Keep it static and add a helper function for access.

//main.c

static int glob_var;
void SetGlobVar(int val) {
  glob_var = val;
}


//file1.c

void SetGlobVar(int);
void foo(void) {
  SetGlobVar(42);
}

Note that the declaration of SetGlobVar() should be put to a header file.

Answer 2

The comments and other answer address the question of how to access and modify a static global" . The following is offed as an alternative to using static for this purpose...

When needing to create a variable that is global and can be changed among several translation units I believe it is more idiomatic to use the extern storage class . This is typically done by:

• Declaring the extern variable in a header file
• Defining the extern variable one-time-only in a .c file that #includes s the header file.
• Access and modify the extern class variable from any translation unit that #include s the header file in which the extern is declared.

Example:

in some.h :

void modify_glob_var(int val);
...
extern int glob_var;//declare extern variable

in main.c

#include "some.h"
...
int glob_var = 0;// define extern variable
...
modify_glob_var(10);//access and modify extern variable

in some_other.c

include "some.h"
...
void modify_glob_var(int val)
{
    glob_var = val;//value of extern glob_var is changed here
}