- What you need to do to
make
global variables
accessible to
(all)
functions in
all program files:
- When global variables are
defined in
some program file:
- All the global variables must be declared (at the top) in all other program files
- When global variables are
defined in
some program file:
- Example:
- Suppose a
C program consists of
3 program files
p1.c, p2.c and p3.c
and has
2 globals variables
x and y:
- Then we must declare them
in other program files
as follows:
In this example, we selectively declare the global variables that are defined in another C program file.
- Suppose a
C program consists of
3 program files
p1.c, p2.c and p3.c
and has
2 globals variables
x and y:
- Problem:
-
Selective declaration is
hard !!!
We need to know which global variables were not defined in a C program file !!!
Need to determine this per C program file !!!
Good news: there is an easier way to declare global variables which I will dicuss next
-
Selective declaration is
hard !!!
- Because you can declare
a variable
as long as the
declaration does
not conflict with
its definition,
it is easier to:
- Declare all global variable in all program files, even when a global variable has been defined in that program file !!!
Example:
- Suppose a
C program consists of
3 program files
p1.c, p2.c and p3.c
and has
2 globals variables
x and y:
- Then we simply declare
all global variables
inside
all program files
as follows:
Even though the global variable x is defined and declared in the program file p1.c, there is no error as long as the declaration and definition do not conflict.
The same is true for the global variable y in the program file p2.c
-
Previously,
we saw this
common practice in
C programming to
declare functions
contained in a C program file with
a header file:
(
click here)
- Write
a header file
prog.h for
each (library)
C source program file prog.c
The header file prog.h will contain:
- The
declarations of
all functions
that are
defined in the C program file
- Some other stuff (now it's time to tell you about the "other stuff") that will be discussed later (specifically: user-defined types and global variables )
- The
declarations of
all functions
that are
defined in the C program file
- Include the
header file
prog.h in
every C program file that
calls
one or more functions defined
in the C program file
prog.c
- This is done to declare the functions so the C compiler will not use implicit function prototyping
- Write
a header file
prog.h for
each (library)
C source program file prog.c
- How to
easily declare the
global variables defined
in a C program file:
- Suppose a
C program consists of
3 program files
p1.c, p2.c and p3.c
and has
2 globals variables
x and y:
- We create a
header file that contains:
- Data type definitions
(if any)
- Function declarations of the functions defined in the C program file
- Variables declarations of the global variables defined in the C program file
Example:
- Data type definitions
(if any)
- Then we simply include
all header files
inside
all program files
as follows:
- Suppose a
C program consists of
3 program files
p1.c, p2.c and p3.c
and has
2 globals variables
x and y: