What does #ifndef Mean?

What does #ifndef Mean?

#ifndef checks whether the given token has been #defined earlier in the file or in an included file; if not, it includes the code between it and the closing #else or, if no #else is present, #endif statement.

What does #ifndef mean in C?

Description. In the C Programming Language, the #ifndef directive allows for conditional compilation. The preprocessor determines if the provided macro does not exist before including the subsequent code in the compilation process.

What is Ifdef and Ifndef?

ifdef means “if the following is defined” while ifndef means “if the following is not defined”.

What is the difference between #if and #ifdef?

#if checks for the value of the symbol, while #ifdef checks the existence of the symbol (regardless of its value).

How do you #define in C++?

C/C++ Pre-processor Commands. 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 #if #endif in C?

The #if directive, with the #elif, #else, and #endif directives, controls compilation of portions of a source file. If the expression you write (after the #if) has a nonzero value, the line group immediately following the #if directive is kept in the translation unit.

What is use of #pragma in C?

The ‘ #pragma ‘ directive is the method specified by the C standard for providing additional information to the compiler, beyond what is conveyed in the language itself. The forms of this directive (commonly known as pragmas) specified by C standard are prefixed with STDC .

What is #ifdef and #endif?

ifdef means “if the following is defined” while ifndef means “if the following is not defined”. So: #define one 0 #ifdef one printf(“one is defined “); #endif #ifndef one printf(“one is not defined “); #endif. is equivalent to: printf(“one is defined “); since one is defined so the ifdef is true and the ifndef is false …

What is #if and #endif in C?

Can Ifdef be nested?

`ifdef and its flavors can be nested one inside the other to create complex ways of code inclusion and exclusion with defined macros.

What does the name STD stand for?

So C++ moved all of the functionality in the standard library into a namespace named “std” (short for standard).

How can I use cout without STD?

We use it by writing using namespace std; then we can access any of the objects like cout, cin….C++

S. No. cout std::cout
1. namespace std must be used in the program Without using namespace std, you should use std::cout.
2. cout is a predefine object of ostream class it is used to print the data as well as values