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What is macro in header file?
A header file is a file containing C declarations and macro definitions (see Macros) to be shared between several source files. You request the use of a header file in your program by including it, with the C preprocessing directive ‘ #include ‘.
Can we define macros in a header file?
Since headers are often the public API of a library, any macros you define in your headers could end up in someone else’s code, doing unexpected things. Not use macros (idiomatic C++ really shouldn’t)
Why should you avoid using directives in a header?
In general, avoid putting using directives in header files (*. h) because any file that includes that header will bring everything in the namespace into scope, which can cause name hiding and name collision problems that are very difficult to debug. Always use fully qualified names in a header file.
How are macros started in a header file?
In a user header file, the macro name should not begin with `_’ . In a system header file, this name should begin with `__’ to avoid conflicts with user programs. In any kind of header file, the macro name should contain the name of the file and some additional text, to avoid conflicts with other header files.
What is the general syntax for accessing the namespace variable?
What is the general syntax for accessing the namespace variable? Explanation: To access variables from namespace we use following syntax. cout< 5.
What is the purpose of this line in a header file #pragma once?
Using #pragma once allows the C preprocessor to include a header file when it is needed and to ignore an #include directive otherwise.
When to use the ifdef directive in a program?
The #ifdef SYMBOL directive is true when SYMBOL has been defined in the code seen so far. If the directive is true, then the statements that come between the #ifdef and an #endif directive later on will be used in the program. If the #ifdef is false, then the statements from that point on will be ignored and not sent to the compiler.
When to use using directive in C + + compiler?
When C++ Standard Library functions and operators are not fully qualified by namespace, or you have not brought the std namespace into the current scope by using a using directive, the compiler can’t find them. To fix this issue, you must either fully qualify the identifier names, or specify the namespace with the using directive.
Where are header guards placed in a file?
Header guards are implemented by using three preprocessor directives in a header file. Two are placed at the beginning of the file, before any pertinent code. The last is placed at the end of the file. The first header guard line is of the form
How many times can a header file be protected?
This insures that the first time through the #ifdef will be the only time that the symbol is undefined. The code being protected will only be seen once, no matter how many times the header file is included. The C style comment after the #endif directive is not mandatory, but it is considered good style.