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Where does global static local register variables free memory and C Program instructions get stored?
Wiki User
∙ 18y ago
* These are all implementation defined. Access to `register' specified indentifiers should be as fast as possible, so the compiler may place the value in a machine register. However, the compiler is free to treat a `register' declaration as an `auto' declaration. * Where free memory is maintained is an OS specific concept. Instructions are generally stored in code segement. Local Variables are stored in Stack. Register variables are stored in Register. Global & static variables are stored in data segment. The memory created dynamically are stored in Heap And the C program instructions get stored in code segment.
Wiki User
∙ 18y ago
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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)
When possible you should advoid using what variables in a program?
Global Variables Or: variables with names longer than 128 characters.
Why memory is divided into initialized and uninitialized areas?
The program's data segment. This area of memory is allocated by the linker and is used to store the program's global variables, static variables, static arrays and constants. Constants are always initialised, as are static variables, but global variables and static arrays need not be initialised.
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.
whose variables are also known as global variables?
The variables which are declared outside the main() function is known as global variables and they can be used anywhere in the program. And, the variables which used declare inside the main() function is known as local variables and they can be used inside the main() function only. Example: #include<stdio.h> #include<conio.h> int x,y; // global variables void main() { int a,b; // Local variables ------------ ---------------------- --------------------- getch(); }
What are global variable?
Variables that are declared globally outside every program are called global variables.
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)
If most variables are local in a program instead of global the result is a program with low or high coupling?
Coupling is the interdependency of a program. A program that uses local variables is more independent than one that uses global variables. Therefore, the program would be considered to have lower coupling.
Which components of program state are shared across threads in a multi-threaded process?
a. Register values b. Heap memory c. Global variables d. Stack memory
When possible you should avoid using variables in a program.?
global
When possible you should advoid using what variables in a program?
Global Variables Or: variables with names longer than 128 characters.
What are the differences between global variables and local variables in C plus plus?
Global variables can be seen in all blocks of your program, when local variables are visible only within the block where it's declared.
When is better to use global variables rather than utilizing local variables in a program?
In my opinion it is rarely a good idea to use global variables, unless you need to refer to them across modules, or their values need to be keep for a long period of program execution. Local variables should always be used when their lifetime is short, usually only in the module they are declared in. Global variables lifetime will be for the length of the program execution.
Why memory is divided into initialized and uninitialized areas?
The program's data segment. This area of memory is allocated by the linker and is used to store the program's global variables, static variables, static arrays and constants. Constants are always initialised, as are static variables, but global variables and static arrays need not be initialised.
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.
whose variables are also known as global variables?
The variables which are declared outside the main() function is known as global variables and they can be used anywhere in the program. And, the variables which used declare inside the main() function is known as local variables and they can be used inside the main() function only. Example: #include<stdio.h> #include<conio.h> int x,y; // global variables void main() { int a,b; // Local variables ------------ ---------------------- --------------------- getch(); }
What is the Conceptual Memory Map of a C Program?
C++ has 4 distinct regions for memory distribution Stack : This region is used for function calls' return addresses , arguments and local variables Heap : This region is for dynamic allocation of memory (dynamic variables created on run time use this memory , aka RAM) Global Variables : This is used for global variables defined by the programmer Program Code : This region is for the program code.
