What is the scope of register variables?

What are register variables?

A register variables is that which got space in CPU internal register sets this requst can be granted or rejected by CPU ,by register veriable the processing speed become much faster for that variable.

What are the different storage class in c?

The four storage classes in C are: automatic, static, external and register. Note that storage classes are not classes in the object-oriented programming sense, they simply define the scope (visibility) of a variable.Automatic Variables (auto)All local variables are automatic by default so we seldom see the auto keyword in code. Local variables are variables declared at function scope.Static Variables (static)All global variables are static by default. Global variables are variables declared at file scope (outside of any function). Static variables can also be explicitly declared inside functions to override the default automatic storage class. All static variables, whether global or local, are allocated within the program's data segment (static memory) and do not fall from scope even if declared locally. All static variables are initialised to zero by default.It's best to avoid the use of global variables unless they are declared constant (const) as it can be difficult to keep track of all the places where a global variable is being operated upon (accessed or assigned to). This can lead to data races in multi-threaded applications unless we take steps to synchronise all access and assignment operations upon the variable. For that reason it's best to keep variables as localised as possible, passing arguments into functions whenever we need to cross scopes. Non-constant global variables should really only be considered if they truly represent a global concept within the file in which they are declared.External Variables (extern)External storage can only be applied to a global variable declared outwith file scope. That is, when a global variable is declared in one file, any external file can gain access to that same global variable simply by declaring the same name and type but with external storage. It follows that external variables are also static variables and is the only case where a variable has two storage classes. Note the local static variables (including local constant variables) cannot be declared external, they are local to the function in which they are declared.This is another reason why it is best to avoid using too many global variables. While we can generally keep track of which code can access a global variable at file scope we have no means of limiting access from outwith that file. Again, prefer local variables to global variables whenever possible.Register Variables (register)A register variable is a variable that we wish to allocate to a CPU register rather than in RAM. Register variables must be no larger than the word-length of the machine and should only be used when we explicitly require fast access to the variable, such as loop counters, accumulators and pointer variables. Note that CPU registers have no address (no identity we can refer to) so we cannot use the unary '&' operator to take the address of a register variable. This means we cannot use pointers to refer to them indirectly which, in turn, means we can only pass them to functions by value (not by reference). However, to do so would defeat the purpose of using the register storage class.Given the limited number of registers available, there is no guarantee that a register variable will actually be allocated to a register; the register keyword is merely a hint to the compiler. It should be noted that modern compilers are extremely good at optimising code so there is seldom any need to explicitly declare register variables.

Memory allocation of variables declared in a program is?

in register

HOW CAN WE REGISTER THE VARIABLES INTO A SESSION?

$_SESSION['name'] = "RAGHAV";

Where do register variables get stored?

Either in registers or on the stack.

Difference between register variable and automatic variables?

Register variables are stored in register of microprocessor/micro-controller. The read/write access to register variable is the fastest because CPU never need any memory BUS operation to access these variable. Auto variable are stored in stack thus access are much slower. Auto variable can be converted to register by using register keyword before it. It has platform specific limitation. Register variable will work only if free registers are available to hold the variable for a function scope. In case of Microprocessor or microcontrollers having very less number of general purpose registers will never take register variable even if we declare it as register.

What is the storage allocation and scope of global extern static local and register variables?

AnswerLocal Variables are stored in Stack. Register variables are stored in Register. Global variables are stored in data segment. The memory created dynamically are stored in Heap And the C program instructions get stored in code segment and the extern variables also stored in data segment. Nooo NoooStatic variable will be stored in .BSS segment... (Block Started By Symbol)

What is meant by delare or initialize a variable or constant at a lowest possible level?

It probably refers to "scope" (see http://en.wikipedia.org/wiki/Scope_(programming)). In programming languages with lexical scope, variables declared in an outer scope can be used in an inner scope, but variables declared in an inner scope cannot be used in outer scopes. It is considered best practice to declare variables (and constants, which are just variables that don't change) at the innermost scope possible for several reasons: # It makes it most clear what the scope of use is of the variable. # It makes it impossible to mistakenly use it in some other location. # It makes it easier to keep track of what variables exist at any given point in the code. For example, in standard C, nested functions are not allowed. This means that in any function, only two types of variables exist - global variables, and variables declared within that function. This has the advantage of making it easy to understand what any variable refers to.

What are register variables What are the advantage of using register variables?

Asks the compiler to devote a processor register to this variable in order to speed the program's execution. The compiler may not comply and the variable looses it contents and identity when the function it which it is defined terminates.

How do you identify the register variables?

Registry variables can be identified with registry allocation. The programmer will decide on the variables that need to be assigned to the registry, and variables not assigned to the registry will be held in RAM.

What is Advantages of register variables in C?

Faster execution of code.

Examples of automatic variables in c?

Automatic variables are variables that are declared within the scope of a block, usually a function. They exist only within that scope, i.e. that block, and they cease to exist after the block is exited. These variables are usually allocated from the stack frame.