How do I use global variables in different files?

If you want to use global variable i of file1.c in file2.c, then below are the points to remember:

1. main function shouldn’t be there in file2.c.
2. now global variable i can be shared with file2. c by two ways: a) by declaring with extern keyword in file2. c i.e extern int i;

Can global variable access in another file?

Variables defined outside of a function are called external variables and can be used by any function in the file, provided only that the function definition follows the variable definition: Variables declared outside of a function are called external, or global,variables and can be accessed by any function.

How do you declare a global variable in C multiple files?

A commonly used C preprocessor trick to handle definition and declaration of global variables. The global variables in a multi-files C program are organized as follows: Each global variable must be defined inside exactly one of the files. Each global variable must be declared inside every C program files.

Are global variables extern by default?

Global variables are not extern nor static by default on C and C++.

Why global variables are bad C++?

Why are global variables bad in C/C++? They hold their values throughout the lifetime of program. They are accessible throughout the execution of program. Non-const global variables are evil because their value can be changed by any function. Using global variables reduces the modularity and flexibility of the program.

Are global variables shared between modules?

Can I have a shared global variable across different files? As we discussed, the global variable is unique to its own module.

How can we create a variable foo to be used globally across all module?

The best way to share global variables across modules across a single program is to create a config module. Just import the config module in all modules of your application; the module then becomes available as a global name.

How do I use global variables in header files?

The clean, reliable way to declare and define global variables is to use a header file to contain an extern declaration of the variable. The header is included by the one source file that defines the variable and by all the source files that reference the variable.

Should I use extern C++?

The extern must be applied in all files except the one where the variable is defined. In a const variable declaration, it specifies that the variable has external linkage. The extern must be applied to all declarations in all files.