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2010-05-25T14:21:06Z

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==A shared resource example.==

<source lang="cpp">
#include <iostream>
#include <cstring>
using namespace std;
class output {
static char sharedResource[255]; // this is the shared resource
static int inuse; // buffer available if 0; in use otherwise
static int oindex; // index of sharedResource
char str[80];
int i; // index of next char in str
int who; // identifies the object, must be > 0
public:
output(int w, char *s) {
strcpy(str, s);
i = 0;
who = w;
}
int putbuf()
{
if(!str[ i ]) { // done outputting
inuse = 0; // release buffer
return 0; // signal termination
}
if(!inuse) // get buffer
inuse = who;
if(inuse != who) // in use by someone else
return -1;
if(str[ i ]) { // still chars to output
sharedResource[oindex] = str[ i ];
i++; oindex++;
sharedResource[oindex] = "\0";// always keep null-terminated
return 1;
}
return 0;
}
void show() {
cout << sharedResource << "\n";
}
};
char output::sharedResource[255]; // this is the shared resource
int output::inuse = 0; // buffer available if 0; in use otherwise
int output::oindex = 0; // index of sharedResource
int main()
{
output object1(1, "This is a test"), object2(2, " of statics");
while(object1.putbuf() | object2.putbuf()) ; // output chars
object1.show();
return 0;
}

</source>

==A static member variable example.==

<source lang="cpp">

#include <iostream>
using namespace std;
class myclass {
static int i;
public:
void setInt(int n) {
i = n;
}
int getInt() {
return i;
}
};

int myclass::i; // Definition of myclass::i. i is still private to myclass.
int main()
{
myclass object1, object2;
object1.setInt(10);
cout << "object1.i: " << object1.getInt() << "\n"; // displays 10
cout << "object2.i: " << object2.getInt() << "\n"; // also displays 10
return 0;
}

</source>

==Init static data before object creation==

<source lang="cpp">
#include <iostream>
using namespace std;
class StaticMemberClass {
static int i;
public:
static void init(int x) {
i = x;
}
void show() {
cout << i;
}
};
int StaticMemberClass::i; // define i
int main()
{

StaticMemberClass::init(100);
StaticMemberClass x;
x.show();
return 0;
}

</source>

==Static function and static variable==

<source lang="cpp">
#include <iostream>
using namespace std;
class MyClass {
static int i;
public:
static void init(int x) {
i = x;
}
void show() {
cout << i;
}
};
int MyClass::i;
int main()
{
// init static data before object creation
MyClass::init(30);
MyClass x;
x.show();
return 0;
}

</source>

==Static function variable==

<source lang="cpp">
#include <iostream>
using namespace std;
void printMessage(void);
int main ()
{
char choice;
do {
cout << "Enter Q to quit, any other character to continue: ";
cin >> choice;
if (choice == "Q")
cout << "Input stopped";
else
printMessage();
} while (choice != "Q");
return 0;
}
void printMessage (void)
{
static int times = 0;
times++;
cout << "This function called " << times << " times\n";
}

</source>

==Static Member Functions: its strictions==

<source lang="cpp">
//A static member function does not have a this pointer.
//cannot be a static and a non-static version of the same function.
//A static member function may not be virtual.
//static functions cannot be declared as const or volatile.
#include <iostream>
using namespace std;
class MyClass {
static int resource;
public:
static int getResource();
void freeResource() {
resource = 0;
}
};
int MyClass::resource; // define resource
int MyClass::getResource()
{
if(resource) return 0; // resource already in use
else {
resource = 1;
return 1; // resource allocated to this object
}
}
int main()
{
MyClass myObject1, myObject2;
if(MyClass::getResource())
cout << "myObject1 has resource\n";
if(!MyClass::getResource())
cout << "myObject2 denied resource\n";
myObject1.freeResource();

if(myObject2.getResource())
cout << "myObject2 can now use resource\n";
return 0;
}

</source>

==Static member functions: "preinitialize" private static data==

<source lang="cpp">
#include <iostream>
using namespace std;
class static_type {
static int i;
public:
static void init(int x) {
i = x;
}
void show() {
cout << i;
}
};
int static_type::i;
int main()
{

static_type::init(100); // init static data before object creation
static_type x;
x.show();
return 0;
}

</source>

==Usage and effect of a static data member==

<source lang="cpp">
#include <iostream>
using namespace std;
class shared {
static int a;
int b;
public:
void set(int i, int j) {
a=i;

b=j;
}
void show();
} ;
int shared::a;
void shared::show()
{
cout << "This is static a: " << a;
cout << "\nThis is non-static b: " << b;
cout << "\n";
}
int main()
{
shared x, y;
x.set(1, 1);
x.show();
y.set(2, 2);
y.show();
x.show();
return 0;
}

</source>

==Use a static member variable independent of any object.==

<source lang="cpp">
#include <iostream>
using namespace std;
class myclass {
public:
static int i;
void setInt(int n) {
i = n;
}
int getInt() {
return i;
}
};
int myclass::i;
int main()
{
myclass object1, object2;

myclass::i = 100; // set i directly, no object is referenced.
cout << "object1.i: " << object1.getInt() << "\n"; // displays 100
cout << "object2.i: " << object2.getInt() << "\n"; // also displays 100
return 0;
}

</source>

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