AcronymDefinition
PPTR Pikes Peak Toll Road
PPTR Pulsed Photothermal Radiometry
PPTR Precision Pressure Transducers Receivers
PPTR Portfolio and Progressive Training Record
PPTR Personal Property Tax Relief
PPTR Progressive Training Record
PPTR pulsed photo-thermal radiometry
PPTR professional pest technician registration
PPTR Program Performance Test Report
PPTR Physiology and Pharmacology of Thermo regulation
PPTR Physiology and Pharmacology of Temperature Regulation
PPTR Parts Per Thousand Report
PPTR Priscilla Pointer
PPTR Portuguese Pointer
PPTR Pudelpointer
PPTR Program Pointer
PPTR Parts Per Trillion Report
PPTR Power Point File format/extension (Microsoft) Report
PPTR Pacific Prevailing Time Report
PPTR Paid Part-Timer Resource
PPTR Papeete, French Polynesia - International Tahiti-Faaa (Airport Code)
Resource
PPTR Partial Prothrombine Time Resource
PPTR Partners for Public Transportation Resource
PPTR Pass Prediction Table Resource
PPTR Patria Para Todos (Homeland for All, political party) Resource
PPTR Pay-Per-Transaction Resource
PPTR Peak Power Tracker Resource
PPTR People's Party of Timor (East Timor) Resource
PPTR Percentage Points (financial reports) Resource
PPTR Personal Productivity Tool (usually meaning a personal computer) Resource
PPTR Personally Procured Transportation Resource
PPTR Physical Prototyping Team Resource
PPTR Pink Poogle Toy (website) Resource
PPTR Planned Parenthood of Toronto Resource
PPTR Planning & Placement Team Resource
PPTR Plunge Protection Team Resource
PPTR Positive Partial Transpose Resource
PPTR Post Production Test Resource
PPTR Postponed (baseball) Resource
PPTR Powered Pallet Truck Resource
PPTR Pre-Production Test Resource
PPTR Precipitate (chemistry) Resource
PPTR Precision Pressure Transducer Resource
PPTR President Pro Tempore Resource
PPTR Presidential Prayer Team Resource
PPTR Primitive Pythagorean Triple (ordered triple of relatively prime integers
that satisfy the Pythagorean theorem) Resource
PPTR Princess Peach Toadstool (Mario Games) Resource
PPTR Principles and Parameter Theory Resource
PPTR Process Project Teams Resource
PPTR Processing Program Table (CICS) Resource
PPTR Product Positioning Time Resource
PPTR Production Prove-out Test Resource
PPTR Professional Poker Tour Resource
PPTR Program Performance Test Resource
PPTR Program Planning Team Resource
PPTR Program Processing Table Resource
PPTR Program Properties Table (MVS Operating System) Resource
PPTR Propagation Prediction Tool Resource
PPTR Public Pay Telephone Resource
PPTR Pulse Pair Timing Resource
PPTR Pulsed Plasma Thruster Resource
PPTR Pupil Personnel Team Resource
PPTR Performance Packet Transmission Rate
PPTR Perfect Painter
PPTR Performance Paper Tape Reader
PPTR Performance Part Time Regular
PPTR Performance Particle Transfer Roller
PPTR Perfect Partner
PPTR Performance Patellar Tendon Reflex
PPTR Performance Pattern-Theoretic Recognition
PPTR Perfect Performance Tuning Request
PPTR Program Philippine Tax Registration
PPTR Performance Pilomatricoma
PPTR Performance Pittsburgh Tribune Review
PPTR Performance Plant Thermal Reduction
PPTR Performance Pneumatic Tyre Roller
PPTR Portable Pointer
PPTR Performance Pool Test Reactor (Chalk River, Ontario; built in 1957, retired
1990)
PPTR Performance Port Thermal Radiator
PPTR Performance Portable Test Range
PPTR Performance Portable Timing Routines
PPTR Performance Pre-Commissioning Test Report (electrical)
PPTR Performance Preliminary Technical Review
PPTR Performance Preliminary Title Report
PPTR Performance Pressure Test Record
PPTR Performance Price to Retailer
PPTR Performance Primary Training Range
PPTR Performance Problem Tracking Report
PPTR Performance Problem Trouble Record
PPTR Performance Problem Trouble Report
PPTR Performance Production Test Requirements
PPTR Performance Production Trial Review
PPTR Performance Production Trial Run
PPTR Performance Program Tape Reader
PPTR Performance Program Technical Report
PPTR Performance Program Trouble Report
PPTR Performance Programa de Transformacion Regional
PPTR Performance Project Team Review
PPTR Performance Project Technical Representative
PPTR Performance Prosperity Through Rice
PPTR Performance Proton Transfer Reaction
PPTR Performance Public Test Realm (gaming, World of Warcraft)
PPTR Performance Public Transport Rate
PPTR Performance Pupil/Teacher Ratio
PPTR Program Pointer
In computer science, a pointer is a programming language data type whose value
refers directly to (or “points to”) another value stored elsewhere in the
computer memory using its address. Obtaining the value to which a pointer refers
is called dereferencing the pointer. A pointer is a simple implementation of the
general reference data type (although it is quite different from the facility
referred to as a reference in C++).
Pointers are so commonly used as references that sometimes people use the word
“pointer” to refer to references in general; however, more properly it only
applies to data structures whose interface explicitly allows it to be
manipulated as a memory address. If you are seeking general information on a
small piece of data used to find an object.
Pointers in data structures
When setting up data structures like lists, queues and trees, it is necessary to
have pointers to help manage the way in which the structure is implemented and
controlled. Typical examples of pointers would be start pointers, end pointers,
or stack pointers.
Architectural roots
Pointers are a very thin abstraction on top of the addressing capabilities
provided by most modern architectures. In the simplest scheme, an address, or a
numeric index, is assigned to each unit of memory in the system, where the unit
is typically either a byte or a word, effectively transforming all of memory
into a very large array. Then, if we have an address, the system provides an
operation to retrieve the value stored in the memory unit at that address.
In the usual case, a pointer is large enough to hold more addresses than there
are units of memory in the system. This introduces the possibility that a
program may attempt to access an address which corresponds to no unit of memory,
either because not enough memory is installed or due to the architecture does
not support such addresses. The first case may, in certain platforms as the
Intel x86 architecture, be called a segmentation fault (segfault). The second
case is possible in the current implementation of AMD64, where pointers are 64
bit long and addresses only extend to 48 bits. There, pointers must conform to
certain rules (canonical addresses), so if a noncanonical pointer is
dereferenced, the processor raises a general protection fault.
On the other hand, some systems have more units of memory than there are
addresses. In this case, a more complex scheme such as memory segmentation or
paging is employed to use different parts of the memory at different times. The
last incarnations of the x86 architecture support up to 36 bits of physical
memory addresses, which were mapped to the 32-bit linear address space through
the PAE paging mechanism. Thus, only 1/16 of the possible total memory may be
accessed at a time. Another example in the same computer family was the 16-bit
protected mode of the ancient 80286 processor, which, though supporting only 16
MiB of physical memory, could access up to 1 GiB of virtual memory, but the
combination of 16-bit address and segment registers made accessing more than 64
KiB in one data structure cumbersome. Some restrictions of ANSI pointer
arithmetic may have been due to the segmented memory models of this processor
family.
In order to provide a consistent interface, some architectures provide
memory-mapped I/O, which allows some addresses to refer to units of memory while
others refer to device registers of other devices in the computer. There are
analogous concepts such as file offsets, array indices, and remote object
references that serve some of the same purposes as addresses for other types of
objects.
Uses
Pointers are directly supported without restrictions in languages such as C,
C++, Pascal and most assembly languages. They are primarily used for
constructing references, which in turn are fundamental to constructing nearly
all data structures, as well as in passing data between different parts of a
program.
In functional programming languages that rely heavily on lists, pointers and
references are managed abstractly by the language using internal constructs like
cons.
When dealing with arrays, the critical lookup operation typically involves a
stage called address calculation which involves constructing a pointer to the
desired data element in the array. In other data structures, such as linked
lists, pointers are used as references to explicitly tie one piece of the
structure to another.
Pointers are used to pass parameters by reference. This is useful if we want a
function's modifications to a parameter to be visible to the function's caller.
This is also useful for returning multiple values from a function.
C pointers
The basic syntax to define a pointer is
int *money;
This declares money as a pointer to an integer. Since the contents of memory are
not guaranteed to be of any specific value in C, care must be taken to ensure
that the address that money points to is valid. This is why it is suggested to
initialize the pointer to NULL
int *money = NULL;
If a NULL pointer is dereferenced then a runtime error will occur and execution
will stop likely with a segmentation fault.
Once a pointer has been declared then, perhaps, the next logical step is to
point it at something
int a = 5;
int *money = NULL;
money = &a;
This assigns the value of money to be the address of a. For example, if a is
stored at memory location of 0x8130 then the value of money will be 0x8130 after
the assignment. To dereference the pointer, an asterisk is used again
*money = 8;
This says to take the contents of money (which is 0x8130), go to that address in
memory and set its value to 8. If a were then accessed then its value will be 8.
This example may be more clear if memory were examined directly. Assume that a
is located at address 0x8130 in memory and money at 0x8134; also assume this is
a 32-bit machine such that an int is 32-bits wide. The following is what would
be in memory after the following code snippet were executed
int a = 5;
int *money = NULL;
Address Contents
0x8130 0x00000005
0x8134 0x00000000
(The NULL pointer shown here is 0x00000000.) By assigning the address of a to
money
money = &a;
yields the following memory values
Address Contents
0x8130 0x00000005
0x8134 0x00008130
Then by dereferencing money by doing
*money = 8;
the computer will take the contents of money (which is 0x8130), go to that
address, and assign 8 to that location yielding the following memory.
Address Contents
0x8130 0x00000008
0x8134 0x00008130
Clearly, accessing a will yield the value of 8 because the previous instruction
modified the contents of a by way of the pointer money.
C arrays
Taking C pointers to the next step is the array.
In C, array indexing is formally defined in terms of pointer arithmetic; that
is, the language specification requires that array[i] be equivalent to *(array +
i). Thus in C, arrays can be thought of as pointers to consecutive areas of
memory, and the syntax for accessing arrays is identical for that which can be
used to dereference pointers. For example, an array array can be declared and
used in the following manner:
int array[5]; /* Declares 5 contiguous integers */
int *ptr = array; /* Arrays can be used as pointers */
ptr[0] = 1; /* Pointers can be indexed with array syntax */
*(array + 1) = 2; /* Arrays can be dereferenced with pointer syntax */
This allocates a block of five integers and declares array as a pointer to this
block. Another common use of pointers is to point to dynamically allocated
memory from malloc which returns a consecutive block of memory of no less than
the requested size that can be used as an array.
While most operators on arrays and pointers are equivalent, it is important to
note that the sizeof operator will differ. In this example, sizeof(array) will
evaluate to 5*sizeof(int) (the size of the array), while sizeof(ptr) will
evaluate to sizeof(int*), the size of the pointer itself.
Default values of an array can be declared like:
int array[5] = {2,4,3,1,5};
If you assume that array is located in memory starting at address 0x1000 on a
32-bit little-endian machine then memory will contain the following:
0 1 2 3
1000 02 00 00 00
1004 04 00 00 00
1008 03 00 00 00
100C 01 00 00 00
1010 05 00 00 00
Representing here are five integers: 2, 4, 3, 1, and 5. These five integers
occupy 32 bits (4 bytes) each with the least-significant byte stored first (this
is a little-endian architecture) and are stored consecutively starting at
address 0x1000.
The syntax for C with pointers is:
* array means 0x1000
* array+1 means 0x1004 (note that the "+1" really means to add one times the
size of array (4 bytes) not literally "plus one")
* *array means to dereference the contents of array which means to consider the
contents as a memory address (0x1000) and to go look up the value at that memory
location (0x1000)
* array[i] means the ith index of array which is translated into *(array + i)
The last example is how to access the contents of array. Breaking it down:
* array + i is the memory location of the ith element of array
* *(array + i) takes that memory address and dereferences it to access the
value.
C linked list
Below is an example of the definition of a linked list in C.
/* the empty linked list is
* represented by NULL or some
* other signal value */
#define EMPTY_LIST NULL
struct link {
/* the data of this link */
void *data;
/* the next link; EMPTY_LIST if this is the last link */
struct link *next;
};
Note that this pointer-recursive definition is essentially the same as the
reference-recursive definition from the Haskell programming language:
data Link a = Nil
| Cons a (Link a)
Nil is the empty list, and Cons a (Link a) is a cons cell of type a with another
link also of type a.
The definition with references, however, is type-checked and doesn't use
potentially confusing signal values. For this reason, data structures in C are
usually dealt with via wrapper functions, which are carefully checked for
correctness.
Pass by reference
Pointers can be used to pass variables by reference, allowing their value to be
changed. For example:
void not_alter(int n) {
n = 360;
}
void alter(int *n) {
*n = 120;
}
void func(void) {
int x = 24;
not_alter(x);
/* x still equal to 24 */
alter(&x);
/* x now equal to 120 */
}
Memory-mapped hardware
On some computing architectures, pointers can be used to directly manipulate
memory or memory-mapped devices. In the mid 80's, using the BIOS to access the
video capabilities of PCs was slow. Applications that were display-intensive
typically used to access CGA video memory directly by casting the hexadecimal
constant 0xB8000000 to a pointer to an array of 80 unsigned 16-bit int values.
Each value consisted of an ASCII code in the low byte, and a colour in the high
byte. Thus, to put the letter 'A' at row 5, column 2 in bright white on blue,
one would write code like the following:
#define VID ((unsigned (*)[80])0xB8000000)
void foo() {
VID[4][1] = 0x1F00 | 'A';
}
Typed pointers and casting
In many languages, pointers have the additional restriction that the object they
point to has a specific type. For example, a pointer may be declared to point to
an integer; the language will then attempt to prevent the programmer from
pointing it to objects which are not integers, such as floating-point numbers,
eliminating some errors.
For example, in C
int *money;
char *bags;
money would be an integer pointer and bags would be a char pointer. The
following would yield a compiler warning of "assignment from incompatible
pointer type" under GCC
bags = money;
because money and bags were declared with different types. To appease the
compiler, it must be made explicit that you do indeed wish to make the
assignment through the use of casting it
bags = (char *)money;
which says to cast the integer pointer of money to a char pointer and assign to
bags.
In languages that allow pointer arithmetic, arithmetic on pointers take into
account the size of the type. For example, adding an integer to a pointer
produces another pointer that points to an address that is higher by that number
times the size of the type. This allows us to easily compute the address of
elements of an array of a given type. This was shown in the example above with C
arrays.
However, few languages strictly enforce pointer types, because programmers often
run into situations where they want to treat an object of one type as though it
were of another type. For these cases, it is possible to typecast, or cast, the
pointer. Some casts are always safe, while other casts are dangerous, possibly
resulting in incorrect behavior. Although it's impossible in general to
determine at compile-time which of these casts are safe, some languages store
run-time type information which can be used to confirm that these dangerous
casts are valid at runtime. Other languages merely accept a conservative
approximation of safe casts, or none at all.
Making pointers safer
Because pointers allow a program to access objects that are not explicitly
declared beforehand, they enable a variety of programming errors. However, the
power they provide is so great that it can be difficult to do some programming
tasks without them. To help deal with their problems, many languages have
created objects that have some of the useful features of pointers, while
avoiding some of their pitfalls.
One major problem with pointers is that, as long as they can be directly
manipulated as a number, they can be made to point to unused addresses or to
data which is being used for other purposes. Many languages, including most
functional programming languages and recent imperative languages like Java,
replace pointers with a more opaque type of reference, typically referred to as
simply a reference, which can only be used to refer to objects and not
manipulated as numbers, preventing this type of error. Array indexing is handled
as a special case.
A pointer which does not have any address assigned to it is called a wild
pointer. Any attempt to use such uninitialized pointers can cause unexpected
behaviour, either because the initial value is not a valid address, or because
using it may damage the runtime system and other unrelated parts of the program.
In systems with explicit memory allocation, it's possible to create a dangling
pointer by deallocating the memory region it points into. This type of pointer
is dangerous and subtle, because a deallocated memory region may contain the
same data as it did before it was deallocated, but may be then reallocated and
overwritten by unrelated code, unbeknownst to the earlier code. Languages with
garbage collection prevent this type of error.
Some languages, like C++, support smart pointers, which use a simple form of
reference counting to help track allocation of dynamic memory in addition to
acting as a reference. In the absence of reference cycles, where an object
refers to itself indirectly through a sequence of smart pointers, these
eliminate the possibility of dangling pointers and memory leaks. Delphi strings
support reference counting natively.
The null pointer
A null pointer has a reserved value, often but not necessarily the value zero,
indicating that it refers to no object. Null pointers are used routinely,
particularly in C and C++ where the compile-time constant NULL is used, to
represent conditions such as the lack of a successor to the last element of a
linked list, while maintaining a consistent structure for the list nodes. This
use of null pointers can be compared to the use of null values in relational
databases and to the “Nothing” value in the “Maybe” monad.
Because it refers to no meaningful object, an attempt to dereference a null
pointer can cause a run-time error that usually terminates the program
immediately (in the case of C, often with a segmentation fault, since the
address literally corresponding to the null pointer will likely not be allocated
to the running program). In Java, access to a null reference triggers a
NullPointerException, which can be caught (but preferred practice is to attempt
to ensure such exceptions never occur). In safe languages a possibly-null
pointer can be replaced with a tagged union which enforces explicit handling of
the exceptional case; in fact, a possibly-null pointer can be seen as a tagged
union with a computed tag.
In C and C++ programming two null pointers are guaranteed to compare equal, ANSI
C guarantees that any NULL pointer will be equal to 0 in a comparison with an
integer type.
A null pointer should not be confused with an uninitialized pointer: a null
pointer is guaranteed to compare unequal to any valid pointer, whereas depending
on the language and implementation an uninitialized pointer might have either an
indeterminate (random or meaningless) value or might be initialised to an
initial constant (possibly but not necessarily NULL).
In most C programming environments malloc returns a NULL pointer if it is unable
to allocate the memory region requested, this notifies the caller that there is
insufficient memory available. However some implementations of malloc allow
malloc(0) with the return of a NULL pointer and instead indicate failure by both
returning NULL and setting errno to an appropriate value.
Computer systems based on a Tagged architecture are able to distinguish in
hardware between a NULL dereference and a legitimate attempt to access a word or
structure at address zero.
Double indirection
In C, it is possible to have a pointer point at another pointer. Although a
higher number of pointer dereferences will add a performance penalty, this can
make manipulating certain data structures particularly neat and elegant. For
instance, consider this code to insert an item into a simple linked list:
struct element {
struct element *next;
int value;
};
struct element *head = NULL;
void insert(struct element *item) {
struct element **p;
for(p = &head; *p != NULL; p = &(*p)->next) {
if(item->value <= (*p)->value) {
break;
}
}
item->next = *p;
*p = item;
}
Wild pointers
Wild pointers are pointers that have not been initialized (that is, set to point
to a valid address) and may make a program crash or behave oddly. In the Pascal
or C programming languages, pointers that are not specifically initialized may
point to unpredictable addresses in memory.
The following example code shows a wild pointer:
int func(void)
{
char *p1 = malloc(sizeof(char)); /* (undefined) value of some place on the heap
*/
char *p2; /* wild (uninitialized) pointer */
*p1 = 'a'; /* This is OK */
*p2 = 'b'; /* ERROR: the result is undefined, and may lead to program crash */
}
Here, p2 may point to anywhere in memory, so performing the assignment *p2 = 'b'
will corrupt an unknown area of memory that may contain sensitive data.
Note that in C and derived languages static variables are safe in this regard. A
static variable without an initializer is initialized to zero on the program's
start.
Support in various programming languages
A number of languages support some type of pointer, although some are more
restricted than others. If a pointer is significantly abstracted, such that it
can no longer be manipulated as an address, the resulting data structure is no
longer a pointer; see the more general reference article for more discussion of
these.
Ada
Ada is a strongly typed language where all pointers are typed and only safe type
conversions are permitted. All pointers are by default initialized to null, and
any attempt to access data through a null pointer causes an exception to be
raised. Pointers in Ada are called access types. Ada 83 did not permit
arithmetic on access types (although many compiler vendors provided for it as a
non-standard feature), but Ada 95 supports “safe” arithmetic on access types via
the package System.Storage_Elements.
C and C++
In C and C++ pointers are variables that store addresses and can be null. Each
pointer has a type it points to, but one can freely cast between pointer types.
A special pointer type called the “void pointer” points to an object of
unspecified type and cannot be dereferenced. The address can be directly
manipulated by casting a pointer to and from an integral type of sufficient size
(not defined in the language itself, but possibly in standard headers).
C++ fully supports C pointers and C typecasting. It also supports a new group of
typecasting operators to help catch some unintended dangerous casts at
compile-time. The C++ standard library also provides auto_ptr, a sort of smart
pointer which can be used in some situations as a safe alternative to primitive
C pointers. C++ also supports another form of reference, quite different from a
pointer, called simply a reference or reference type.
Pointer arithmetic, that is, the ability to modify a pointer's target address
with arithmetic operations (as well as magnitude comparisons), is restricted by
the language standard to remain within the bounds of a single array object (or
just after it), though many non-segmented architectures will allow for more
lenient arithmetic. Adding or subtracting from a pointer moves it by a multiple
of the size of the datatype it points to. For example, adding 1 to a pointer to
4-byte integer values will increment the pointer by 4. This has the effect of
incrementing the pointer to point at the next element in a contiguous array of
integers -- which is often the intended result. Pointer arithmetic cannot be
performed on void pointers because the void type has no size, and thus the
pointed address can not be added to. For working 'directly' with bytes they
usually cast pointers to BYTE*, or unsigned char* if BYTE isn't defined in the
standard library used.
Pointer arithmetic provides the programmer with a single way of dealing with
different types: adding and subtracting the number of elements required instead
of the actual offset in bytes. (though the char pointer, char being defined as
always having a size of one byte, allows the element offset of pointer
arithmetic to in practice be equal to a byte offset) In particular, the C
definition explicitly declares that the syntax a[n], which is the n-th element
of the array a, is equivalent to *(a+n), which is the content of the element
pointed by a+n. This implies that n[a] is equivalent to a[n].
While powerful, pointer arithmetic can be a source of computer bugs. It tends to
confuse novice programmers, forcing them into different contexts: an expression
can be an ordinary arithmetic one or a pointer arithmetic one, and sometimes it
is easy to mistake one for the other. In response to this, many modern high
level computer languages (for example Java) do not permit direct access to
memory using addresses. Also, the safe C dialect Cyclone addresses many of the
issues with pointers. See C programming language for more criticism.
The void pointer, or void*, is supported in ANSI C and C++ as a generic pointer
type . A pointer to void can store an address to any data type, and, in C, is
automatically cast to any other pointer type on assignment, but it must be
explicitly cast if dereferenced inline. K&R C used char* for the “type-agnostic
pointer” purpose.
int x = 4;
void* q = &x;
int* p = q; /* void* automatically cast to int*: valid C, but not C++ */
int i = *p;
int j = *((int*)q); /* when dereferencing inline, there is no automatic casting
*/
C++ does not allow the automatic casting of void* to other pointer types, not
even in assignments. This was a design decision to avoid careless and even
unintended casts, though most compilers only output warnings, not errors, when
encountering other ill casts.
int x = 4;
void* q = &x;
// int* p = q; // This fails in C++: there is no autocast from void*
int* a = (int*)q; // C-style cast
int* b = static_cast<int*>(q); // C++ cast
In C++, there is no void& (reference to void) to complement void* (pointer to
void), because references behave like aliases to the variables they point to,
and there can never be a variable whose type is void.
C#
In the C# programming language, pointers are supported only under certain
conditions: any block of code including pointers must be marked with the unsafe
keyword. Such blocks usually require higher security permissions than
pointerless code to be allowed to run. The syntax is essentially the same as in
C++, and the address pointed can be either managed or unmanaged memory. However,
pointers to managed memory (any pointer to a managed object) must be declared
using the fixed keyword, which prevents the garbage collector from moving the
pointed object as part of memory management while the pointer is in scope, thus
keeping the pointer address valid.
The .NET framework includes many classes and methods in the System and
System.Runtime.InteropServices namespaces (such as the Marshal class) which
convert .NET types (for example, System.String) to and from many unmanaged types
and pointers (for example, LPWSTR or void*) to allow communication with
unmanaged code.
D
The D programming language is a derivative of C and C++ which fully supports C
pointers and C typecasting. However D also offers numerous constructs such as
foreach loops, out function parameters, reference types, and advanced array
handling which replace pointers for most routine programming tasks.
Fortran
Fortran-90 introduced a strongly-typed pointer capability. Fortran pointers
contain more than just a simple memory address. They also encapsulate the lower
and upper bounds of array dimensions, strides (for example, to support arbitrary
array sections), and other metadata. An association operator, => is used to
associate a POINTER to a variable which has a TARGET attribute. The Fortran-90
ALLOCATE statement may also be used to associate a pointer to a block of memory.
For example, the following code might be used to define and create a linked list
structure:
type real_list_t
real :: sample_data(100)
type (real_list_t), pointer :: next => null ()
end type
type (real_list_t), target :: my_real_list
type (real_list_t), pointer :: real_list_temp
real_list_temp => my_real_list
do
read (1,iostat=ioerr) real_list_temp%sample_data
if (ioerr /= 0) exit
allocate (real_list_temp%next)
real_list_temp => real_list_temp%next
end do
Fortran-2003 adds support for procedure pointers. Also, as part of the C
Interoperability feature, Fortran-2003 supports intrinsic functions for
converting C-style pointers into Fortran pointers and back.
BASIC
BASIC does not support pointers. Some dialects of BASIC, including FreeBASIC,
have exhaustive pointer implementations, however.
This short section requires expansion.
Modula-2
Pointers are implemented very much as in Pascal, as are VAR parameters in
procedure calls. Modula 2 is even more strongly typed than Pascal, with fewer
ways to escape the type system. Some of the variants of Modula 2 (such as
Modula-3) include garbage collection.
Oberon
Much as with Modula-2, pointers are available. There are still fewer ways to
evade the type system and so Oberon and its variants are still safer with
respect to pointers than Modula-2 or its variants. As with Modula-3, garbage
collection is a part of the language specification.
Pascal
Pascal implements pointers in a straightforward, limited, and relatively safe
way. It helps catch mistakes made by people who are new to programming, like
dereferencing a pointer into the wrong datatype; however, a pointer can be cast
from one pointer type to another. Pointer arithmetic is unrestricted; adding or
subtracting from a pointer moves it by that number of bytes in either direction,
but using the Inc or Dec standard procedures on it moves it by the size of the
datatype it is declared to point to. Trying to dereference a null pointer, named
nil in Pascal, or a pointer referencing unallocated memory, raises an exception
in protected mode. Parameters may be passed using pointers (as var parameters)
but are automatically handled by the static compilation system.
PPTR Pulsed Photothermal Radiometry
Pulsed Photothermal Radiometry (PPTR) measures blackbody radiation
emitted by a sample after absorption of an optical pulse. Photothermal effect is
a phenomenon associated with electromagnetic radiation. It is produced by the
photoexcitation of material, resulting in the production of thermal energy
(heat).
It is sometimes used during treatment of blood vessel lesions, laser
resurfacing, laser hair removal and laser surgery. In pulsed photothermal
profiling of human skin, subsurface blood vessels may be difficult to resolve
due to nonselective absorption in the overlying epidermis.
PPTR Personal Property Tax Relief
Qualifying vehicles include passenger vehicles, motorcycles and pickup and
panel trucks with a gross weight of 7,500 pounds or less that are predominantly
used for personal use and are either privately owned or leased where the lessee
pays the personal property tax.
Effective January 1, 2006, each county, city and town was given the authority to
determine the amount of tax relief on qualified vehicles. Per changes to the
Personal Property Tax Relief Act, delinquent tax bills for tax years 2001-2005
that remain unpaid as of September 1, 2005, will require the taxpayer to pay
100% of the original tax plus or including penalty and interest charges.
Physiology and Pharmacology of Temperature Regulation
The Integrated Meeting on the Physiology and Pharmacology of Temperature
Regulation (PPTR) is held every two to three years. This seminal meeting
originated from two independent, and long-running symposia.
The first to be initiated was the Thermal Physiology Symposium, which had its
inaugural meeting in New Haven (U.S.A.) in 1968, and was organised by James
Hardy. This was the legendary meeting known from the famous book, “Physiological
and Behavioral Temperature Regulation” (1970). Since then, the Thermal
Physiology Symposium was held as a satellite meeting of the IUPS main congress.
The last independent Thermal meeting in this series was held in 2001
(Wollongong, Australia).
The second series of conferences was the Symposium on the Pharmacology of
Thermoregulation, first held in1972 (San Francisco, U.S.A.), and organised by Ed
Schonbaum and Peter Lomax. This series of meetings arose from the increasing
recognition of the strong relationship between pharmacology and
thermoregulation. This symposium continued every three years, independently of
the Thermal Physiology Symposium, with the last conference from this series
being held in 1999 (Seville, Spain).
However, since pharmacological methods have become more and more important in
the study of physiological mechanisms, and since physiology is, of course, the
basis of pharmacological research, many researchers attended both meetings.
Furthermore, since the IUPS main congress became quadrennial instead of
triennial since 1993, it became increasingly difficult to set the timing of the
two independent series of symposia. Thus, the merger of the two conferences was
decided at the Pharmacology meeting in 1999.
The First Integrated Meeting on Thermal Physiology and Pharmacology of
Thermoregulation (PPTR) was successfully held in 2004 (Rhodes, Greece), thanks
to the time, energy and expertise invested by its organisers, and about 200
scientists gathered on that beautiful island in the Aegean Sea. The Second PPTR
Symposium was held in Phoenix (U.S.A.), with the Third PPTR Symposium planned
for Matsue (Japan) in July 2009, as a satellite meeting of the 38th IUPS
Congress (Kyoto, July, 2009).
After the 2001 Thermal Physiology Symposium, and due also to the overlapping
interests with scientists attending the International Conference on
Environmental Ergonomics, it was decided to more closely align these independent
conferences. Now conferences from each group are scheduled to facilitate
attendance at both meetings, with each conference offering a wide range of
dedicated sessions applicable to thermal physiologists, pharmacologists and
ergonomists.

Are you interested in
mult-player online internet games? Such as runescape and neopets?Internet
Game Online-games, tips, cheats and kids forumsAnother
good forum is the Internet Junction For Gamers IJFG.COM
Internet Junction For Gamers, Runescape Market and
More IJFG.COM Jokes, Pranks, Runescape and other cool games at IJFG.COM.
RuneScape is set in a medieval fantasy world, similar to "Guild Wars" or
"EverQuest", where players control character representations of themselves. As
with most massive multiplayer online roleplaying games (MMORPG), there is no
overall objective or end to the game. Players explore, form alliances, perform
optional tasks, and complete quests for rewards and to build character's skills.

RuneScape has often been one of
the top massive online role playing games. It is a unique game. But, with a
unique game, comes unique players. Players get bored, and then try to develop
cheats....autos or bots that will help them achieve success in their beloved
games of Runescape 2.
RuneScape is a virtual world which
is divided into two part: Members Areas and Non-Members areas. People who pay to
play (p2p), receive access to the special areas. They also have access to the
free areas. The members' places are much larger, offer "better" items for the
gameplay of rs2, and much, much more. The character that you create when you
first start playing runescape, moves around the game on foot; either by running,
or walking. Players are challenged to their utmost skills by fighting new
monsters, completing difficult quests, and manipulating marketing. As Runescape
2 is an RPG (Role playing game), there is no set path a person must take to play
rs. They can choose what to do, and when, whether it be training their
money-making skills, or fighting another player. Players usually interact with
each other by chatting through public chat, or private chat.Internet
Junction For Gamers, Runescape Market and More IJFG.COM IJFG.com was a
runescape 2 based site. They have now, however, taken another look....
Of course the king of all game
cheating websites is
trick
the trik (otherwise known as RPG Cheats Site), where you can find cheat
forums, mmorpg topsite, arcade games and any mmo game related topics.
The master of massive multiplayer
online role-playing games (MMORPG) cheats can be found at Trik.com
Trik.com; this site is one of the best today. The forum section,
Trik.com forum, originally came from IJFG.com (Internet Junction For
Gamers) , which was one of the best websites that discussed various gamers'
issues. The full name was Internet Junction For Gamers, Runescape Market and
More. This site had Jokes, Pranks, RuneScape and other cool games. RuneScape is
set in a medieval fantasy world, similar to "Guild Wars" or "EverQuest," where
players control character representations of themselves. As with most MMORPG,
there is no overall objective or end to the game. Players explore, form
alliances, perform optional tasks, and complete quests for rewards and to build
characters' skills.
Trik.com continues IJFG.com's
success, but Trik.com has more to offer. Trik Topsite can be found at
Trik Topsite; the TopSite is a great addition if you want to find the best
MMO RPG site(s) or raise your site in the rankings. Trik.com also has a
viciously competitive Arcade. If you want to be the #1 Arcade on Trik, then come
prove yourself at Trik.com arcade:
Trik arcade. Trik.com ?Trik.com/topsite ?Trik.com/forum/arcade.php
With the rising popularity of
commercial MMORPG games came the desire from ardent players of these games to
run their own servers beside the ones run by the game's creator. Since the
original server software is not usually available, the behavior of the server
has to be re-engineered. This can be done by analyzing the data stream with the
original server, or by disassembling and analyzing the client which is
available.
Ultima Online was one of the first
large MMORPGs. Due to its openness in implementation, server emulators arose
very quickly, even during the beta stage of development. The destination to
which the client connects was changeable by simply editing a text file. In beta
stage the client-server data stream was not encrypted yet. The term server
emulator became known through Ultima Online server reimplementation such as UOX,
which was the pioneer. Many forks and reimplementations followed UOX, because
its source code was released under the GNU General Public License relatively
early. RunUO is today the most widely used UO-server emulator. After RuneScape
implemented anti-cheating measures, many gamers left and started their own
private servers. The best place to discuss the private server is at
Trik- The Master of Private Server.
Another useful site is
Rune
Web ruwb.com . This site is about more serious RuneScape gold trading,
account exchange, gold for real life cash and many services. It includes tips on
how to avoid getting lured/scammed while using the marketplace. For programming,
visual basics, java, C/C++, scar and all other languages such as PHP, HTML, ASP,
Delphi. There are also sections for graphics talents, plus many cool videos and
fun stuff.
A defining moment in internet
gaming history was when a group of gamers called (hygo 7) decided to start an
ultimate game forum, which they named
hygo.com. It has the best financial backing, the friendliest game community,
and the highest quality of information. Currently Hygo.com has entered a new
phase...Hygo.com is offering the best private server game. With thousands of
members, Hygo.com is your next place to visit, as they have an amazing game with
a community and economy.
Hygo.com - The Online Adventure Game. is definitely one of the top sites you
want to join right now!
EZud is another popular site.
ezud.com. It has the best runescape bug abuse, bugs and trik.
ezud.com - The runescape bugs. is definitely one of the best sites you want
to join right now!
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