Use of static and extern in C Language

Under the big project, we will encounter many source documents.

Document a. c

Static int I; // only used in document

Int j; // used in the project

Static void init () // only used in document

{

}

Void callme () // used in the project

{

Static int sum;

}

The above global I variables and init () functions can only be used in document a. c, and the scope of global variable sum is only in callme. The limitations of variable j and function callme () are extended to the entire project document. Therefore, the following B. c can be called with the extern keyword. Extern tells the compiler that this variable or function has been defined in other documents.

Document B .C

Extern int j; // call

Extern void callme (); // call

Int main ()

{

...

}

In addition, when C and C ++ are mixed programming, if c ++ calls a function or variable defined in the c source document, so we need to add extern to tell the compiler to name the function in c mode:

Document A. cpp calls the variables I and callme () in a. c ()

Extern "C" // call the variable in c document in c ++ document

{

Int j;

Void callme ();

}

Int main ()

{

Callme ();

}

Ii. static rules:

A. if the global variable is only accessed in A single C document, the variable can be changed to A static global variable. tbw can reduce the coupling between modules;

B. If the global variable is only accessed by a single function, the variable can be changed to the static local variable of the function to reduce the coupling between modules;

C. When designing and using functions that access dynamic global variables, static global variables, and static local variables, you need to consider re-import;