- C has five (5)
kinds of variables - divided into
2 categories:
- "Long term" variables:
(a.k.a.:
compile-time (allocated)
variables)
- Global variables --- accessible everywhere
- Static global variables --- accessible within all functions defined inside the same C program file
- Static local variables --- accessible within the one C function
Common property:
- The life time of these kinds of variables is the whole execution period of the C program
- Short term variables:
(a.k.a.: run-time variables)
- Local variables
- Parameter variables
Common property:
- The memory space used for
these kinds of variables
are allocated (reserved)
during the
execution (running) of the program
- They are created on the system stack (just like what you learned in assembler programming !!!)
- "Long term" variables:
(a.k.a.:
compile-time (allocated)
variables)
- Just like Java, the
location (place) where the
variable is defined
in the (C) program determines
the kind of variable
that will be defined:
- Parameter variables
are defined inside the
braces ( ... )
of the function header
Example:
int main( int argc, char *argv[] ) { ^^^^^^^^^^^^^^^^^^^^^^^^ parameter variables ... ... }(Just like Java)
- Local variables
are defined inside the
body of a function
(i.e., between the
braces { ... }
of the function body)
Example:
int main( int argc, char *argv[] ) { int a; double b; ^^^^^^^^^^^^ local variables ... if ( .... ) { int x; ^^^^^^^^^^ local variable } ... }(Just like Java)
- Global variables
are defined outside a
function
without using
the keyword
static:
int a; // Global variable int b; // Global variable int main ( int argc, char *argv[] ) { ... ... } double c; // Global variable void f( .... ) { ... ... }
(The 2 different kinds of global variables are distinguished by the static keyword.)
- Static global variables
are defined outside a
function
using
the keyword
static:
static int a; // Static global variable static int b; // Static global variable int main ( int argc, char *argv[] ) { ... ... } double c; // Global variable void f( .... ) { ... ... }
(The 2 different kinds of global variables are distinguished by the static keyword.)
- Static (local) variables
are defined inside a
function using the
keyword static:
int main ( int argc, char *argv[] ) { static double d; // Static variable double f; // Normal local variable ! ... ... } double c; // Global variable void f( .... ) { ... ... }
- Parameter variables
are defined inside the
braces ( ... )
of the function header
- Summary:
