Question: What Is The Difference Between #Define And Const?

Does Const improve performance?

const correctness can’t improve performance because const_cast and mutable are in the language, and allow code to conformingly break the rules.

That said, it is trivial for the compiler to look at the code it generates and determine if it actually writes to a given variable, and apply optimizations accordingly..

Why are macros bad?

The trouble with macros is that they are processed before your c/c++ code and generate new code that can be faulty and cause compiler errors which are all but obvious.

What is a #define in C?

In the C Programming Language, the #define directive allows the definition of macros within your source code. These macro definitions allow constant values to be declared for use throughout your code. … You generally use this syntax when creating constants that represent numbers, strings or expressions.

Can we use const and static together?

Const : is a type qualifier. … So combining static and const, we can say that when a variable is initialized using static const, it will retain its value till the execution of the program and also, it will not accept any change in its value.

What is difference between const and static?

const is just constant, meaning can’t be modified. Static variables are common across all instances of a type. constant variables are specific to each individual instance of a type but their values are known and fixed at compile time and it cannot be changed at runtime.

Why is C so powerful?

One powerful reason is memory allocation. Unlike most programming languages, C allows the programmer to write directly to memory. Key constructs in C such as structs, pointers and arrays are designed to structure and manipulate memory in an efficient, machine-independent fashion.

Why is Typedef used in C?

typedef is a reserved keyword in the programming languages C and C++. It is used to create an additional name (alias) for another data type, but does not create a new type, except in the obscure case of a qualified typedef of an array type where the typedef qualifiers are transferred to the array element type.

What is Const used for?

The const keyword allows you to specify whether or not a variable is modifiable. You can use const to prevent modifications to variables and const pointers and const references prevent changing the data pointed to (or referenced).

Can #define value be changed?

You can’t change a #define like that. If you want to change the value throughout your program just make it a variable ( local or global ) and then change it. When you have a #define the whole idea is that it is constant for the life of the program. You cannot modify that value.

What is micro in C?

MicroC is the powerful C compiler integrated in Super-Flash which produces programs which can be run not only by Super-Flash applications, but others as well. … MicroC is a powerful compiler independent of the hardware, is simple and reliable, rich in functions and performances.

When to use #define vs Const?

const and #define both are used for handle constants in source code, but they few differences. #define is used to define some values with a name (string), this defined string is known as Macro definition in C, C++ while const is a keyword or used to make the value of an identifier (that is constant) constant.

What to use instead of #define in C++?

If you accidentally redefine a name with a #define , the compiler silently changes the meaning of your program.

Which is better #define or enum and why?

18 Answers. enum defines a syntactical element. #define is a pre-preprocessor directive, executed before the compiler sees the code, and therefore is not a language element of C itself. Generally enums are preferred as they are type-safe and more easily discoverable.

What is #define used for in C++?

The #define command is used to make substitutions throughout the file in which it is located. In other words, #define causes the compiler to go through the file, replacing every occurrence of macro-name with replacement-string. The replacement string stops at the end of the line.

What is the advantage of define over Const?

#define is a preprocessor directive. Things defined by #define are replaced by the preprocessor before compilation begins. const variables are actual variables like other normal variable. The big advantage of const over #define is type checking.

Why is #define used?

The #define directive is used to define values or macros that are used by the preprocessor to manipulate the program source code before it is compiled. Because preprocessor definitions are substituted before the compiler acts on the source code, any errors that are introduced by #define are difficult to trace.

When should I use const?

4 AnswersAlways use const for function parameters passed by reference where the function does not modify (or free) the data pointed to. … Always use const for constants that might otherwise be defined using a #define or an enum. … Never use const in a function prototype for a parameter passed by value.More items…•

What is meant by preprocessor?

In computer science, a preprocessor is a program that processes its input data to produce output that is used as input to another program. … A common example from computer programming is the processing performed on source code before the next step of compilation.

Where are macros stored in memory?

Macros are not stored in memory anywhere in the final program but instead the code for the macro is repeated whenever it occurs. As far as the actual compiler is concerned they don’t even exist, they’ve been replaced by the preprocessor before they get that far.

What is the difference between macro and constant in C?

4 Answers. Macros are handled by the pre-processor – the pre-processor does text replacement in your source file, replacing all occurances of ‘A’ with the literal 8. Constants are handled by the compiler. … For the actual compiled code, with any modern compiler, there should be zero performance difference between the two …

How do you use const?

The const keyword can also be used in pointer declarations. A pointer to a variable declared as const can be assigned only to a pointer that is also declared as const . You can use pointers to constant data as function parameters to prevent the function from modifying a parameter passed through a pointer.