Skip to main content

C++ Preprocessor

C++ Preprocessor

Preprocessor directives are one of the unique features of C++. It provides many tools that other high-level language does not, and programmers can use these tools to create efficient, easy-to-read, easy-to-modify and portable C ++ programs.
Before a C++ program gets compiled by the compiler, the source-code gets processed by the compiler. This technique is called preprocessor and the process is called preprocessing. It is separate program part that the C++ compiler invokes it at the first part of the translation. This technique is not a part of the compiler but it is a separate method that comes under compilation process. It directs the compiler that the information should be preprocessed before the actual compilation starts.
All preprocessor directives in C++ begin with #, and they do not need to end with a semicolon(;) because this is not a statement in C++.
The #define directive creates a symbolic constants and these symbolic constants are called macro.
The general form of the directive is:
Syntax:
#define macro-name replacement-text

Simple Program of Preprocessor Directive

Example:
#include<iostream> 
#define val 12

using namespace std;

int main()
{
    cout << "Value is :" << val << endl;
}
There are different preprocessor directives that perform different tasks. You can categorize these Preprocessor Directives as follows:
  • Inclusion Directives:
    • #include: specifies the files to be included, especially header-files
  • Macro Definition Directives:
    • #define: define a macro substitution
    • #undef: It is used for undefining a macro
  • Conditional Compilation Directives:
    • #if: It tests a compile-time condition
    • #elif
    • #endif: It specify the end of #if
    • #ifdef: It is used to test for macro definition
    • #ifndef: It tests whether a macro is not defined
    • #else: It provides an alternative option when #if fails
  • Other Directives:
    • #error
    • #line: Supplies a line number for compiler messages
    • #pragma: It specifies implementation-defined instructions to the compiler
Labels:

Comments

Post a Comment

For Programs Click Here

Programs

Popular posts from this blog

Python Lists

Python Lists Dealing with data in a structured format is quiet generous, and this is possible if those data are set accordingly in a specific manner. So, Python provides these data structures named ‘lists’ and ‘tuples’ that are used to organize data in  single set. Python has 6 built-in sequences and among them the most famous are “lists and tuples”. The lists are containers that hold a number of other objects in a given order. It usually puts into practice the sequence protocol and allows programmers to add or remove objects from that sequence. Each element of the sequence is assigned a number i.e. he index and the first index is 0 (zero). This versatile data-type of Python is written in a sequence of list separated by commas between expressions. Creating Lists To build a list, just put a number of expressions in square brackets. The syntax is: Syntax: lst1 = [ ] # lst1 is the name of the list lst2 = [ expression1 , …. , expression_N ] Example: #!/usr/bin/python ls...
Post a Comment
Read more

C++ Qualifiers and Storage Classes

C++ Qualifiers and Storage Classes Qualifiers and storage class are smaller but important programming concept that helps to make the quality of a variable more accurate for using that variable within the program. In this chapter you will learn about how qualifiers are used with variables and what the roles of different storage classes in C++ are. What is a Qualifier? A qualifier is a token added to a variable which adds an extra  quality , such as specifying volatility or constant-ness to a variable. They act like an adjective for a variable. With or without a qualifier, the variable itself still occupies the same amount of memory, and each bit has the same interpretation or contribution to the state/value. Qualifiers just specify something about how it may be accessed or where it is stored. Three qualifiers are there in C++. These are: const : This is used to define that the type is constant. volatile : his is used to define that the type is volatile. mutable:  applies to non...
Post a Comment
Read more

Syllabus

Syllabus  C Programming Tutorials C Tutorial C Introduction History of C Programming Language C Installation C Program Structure C Input and Output (I/O) C Format Specifiers Declaration & Assignments C Tokens C Identifiers C Keywords C Constants C Operators C Data Types C Variables C Preprocessors C Type Casting C Custom Header File Flow Control C Decision Making C if Statements C if-else Statements C Nested if-else Statements C else-if Statements C goto Statement C switch Statements C Loops C while loops C do while loops C for loops Functions C Functions C Function Arguments C Library Functions C Variable Scope Arrays & Strings C Arrays C Strings Pointers C Pointers C Dynamic Memory Allocation Structure & Union C Structures C Unions File I/O C File Handling C fopen C fclose C getc C putc C getw C putw C fprintf C fscanf C fgets C fputs C feof                                     ...
3 comments
Read more