Declaration of any variable or a function means that your are specifying that the following variable or funtion will be used in your program. Where as in definition you exactly specify the value or some properties of the variable or the function.
For Example: For declaration of any user defined function 'say, addition the syntax is: int addition ; Here the above line specifies that the function is an integer function, addition is the name of this function and semicolon after the specifies that this is a declaration. In C language the function definition and declaration is generally done on the top of the main program. Other Related Discussions. Please Help. Need help in doing a simple "crossword" between two words.
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Missing Affiliations: Undisclosed relationship to topics. Other: Other flag. Follow Us. The values of num1 and num2 are calculated and assigned to the result variable. Finally, the sum displays on the console. The definition of a variable indicates the compiler where and how much storage to create for the variable.
A variable definition defines the data type and a set of one or more variables of that type. Below is an example of a declaration. It declares and defines the variables a and b. It tells the compiler to create three integer variables called a and b. Initialization is the process of assigning initial values to the variables. It is also possible to initialize values to the variables in the declaration. An example is as follows.
The declaration is a statement that assures the compiler of the existing variable so that the compiler can proceed for further compilation without requiring the complete details about the variable.
On the other hand, the definition is a statement that explains the compiler on where and how much storage to create for the variable. Declaration is different from definition because it gives information used only by the compiler. We can say that declaration is an information used by the compiler to establish the correct use of the variable and for how long some memory belongs to certain variable.
Find similar answers here: Technical Interview Questions in C. A declaration provides a name to the program; a definition provides a unique description of an entity e. Declarations can be repeated in a given scope, it introduces a name in a given scope. Couldnt you state in the most general terms possible, that a declaration is an identifier in which no storage is allocated and a definition actually allocates storage from a declared identifier?
One interesting thought - a template cannot allocate storage until the class or function is linked with the type information. So is the template identifier a declaration or definition? It should be a declaration since no storage is allocated, and you are simply 'prototyping' the template class or function. This is going to sound really cheesy, but it's the best way I've been able to keep the terms straight in my head:. Declaration: Picture Thomas Jefferson giving a speech A declaration presents a symbol name to the compiler.
A definition is a declaration that allocates space for the symbol. In C, a declaration merely provides information that a function or variable exists and gives its type. For a function declaration, information about the types of its arguments might be provided as well.
The purpose of declarations is to allow the compiler to correctly process references to the declared variables and functions. A definition, on the other hand, actually allocates storage for a variable or says what a function does. Declaration of a variable is for informing to the compiler the following information: name of the variable, type of value it holds and the initial value if any it takes.
Whereas, Definition of a variable says where the variable gets stored. The concept of Declaration and Definition will form a pitfall when you are using the extern storage class because your definition will be in some other location and you are declaring the variable in your local code file page. You can declare at a place of your choice. A class or struct allows you to change how objects will be defined when it is later used.
For example. When we learn programming these two terms are often confused because we often do both at the same time. It is important to distinguish between the declaration of an external variable and its definition. A declaration announces the properties of a variable primarily its type ; a definition also causes storage to be set aside. If the lines.
There must be only one definition of an external variable among all the files that make up the source program. Array sizes must be specified with the definition, but are optional with an extern declaration.
Declarations specify the interpretation given to each identifier; they do not necessarily reserve storage associated with the identifier. Declarations that reserve storage are called definitions. The declaration is when a primitive or object reference variable or method is created without assigning value or object. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. What is the difference between a definition and a declaration? Ask Question. Asked 12 years, 2 months ago. Active 8 months ago. Viewed k times. The meaning of both eludes me. Improve this question. MD XF 7, 7 7 gold badges 36 36 silver badges 64 64 bronze badges. Maciek Maciek Frankly, I had a lot of trouble learning which was which, so I didn't find the names obvious.
I had no problem with the meanings, just which names to associate with the meanings. We've been over this in exhaustive detail: stackoverflow. DavidThornley I use this trick: a definition gives a finer description of a given variable or function. To remember this, I recall that the middle of the word "definition" has a resemblance to the word "finer". MarcoLeogrande: Or "definite"! Show 5 more comments. Active Oldest Votes. Amongst them: [Example: [ Improve this answer. Community Bot 1 1 1 silver badge.
For example, 6. Brian: "extern int i;" says that i is an int somewhere, don't worry about it. Brian: You're wrong. You can have as many extern int i in each compilation unit as you want. It denotes the space for the integer to be in this translation unit and advices the linker to link all references to i against this entity.
If you have more or less than exactly one of these definitions, the linker will complain. These amount to the same thing, which is what sbi says: in both cases this declaration specifies the object to which all references to "i" in that scope must be linked. It's allowed elsewhere though. What is a definition and what a declaration has subtle rules when it comes to templates - beware! Show 25 more comments. Felipe Augusto 6, 7 7 gold badges 29 29 silver badges 64 64 bronze badges.
Michael Kristofik Michael Kristofik RJFalconer You're correct; initialization does not necessarily turn a declaration into a definition contrary to what one might expect; certainly I found this surprising. Your modification to the example is actually illegal unless b is also declared const.
See stackoverflow. This is interesting to me. Different ways to look at it, I suppose. Declaration is for the compiler to accept a name to tell the compiler that the name is legal, the name is introduced with intention not a typo. Definition is where a name and its content is associated. The definition is used by the linker to link a name reference to the content of the name. Add a comment.
Declaration: "Somewhere, there exists a foo. Johannes Schaub - litb Johannes Schaub - litb k gold badges silver badges bronze badges. Declaration Declarations tell the compiler that a program element or name exists.
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