How do you define a string macro?

We can create two or more than two strings in macro, then simply write them one after another to convert them into a concatenated string. The syntax is like below: #define STR1 “str1″ #define STR2 ” str2″ #define STR3 STR1 STR2 //it will concatenate str1 and str2.

What does preprocessor do on macro call?

The preprocessor provides the ability for the inclusion of header files, macro expansions, conditional compilation, and line control. In many C implementations, it is a separate program invoked by the compiler as the first part of translation.

What is __ Va_opt __?

The sequence __VA_OPT__(x) , which is only legal in the substitution list of a variable-argument macro, expands to x if __VA_ARGS__ is non-empty and to nothing if it is empty. That allows us to fix the LOG macro by suppressing the comma when the argument list is empty: #define LOG(fmt.)

What is macro replacement?

The macro substitution is a process where an identifier in a program is replaced by a predefined string or a value. Different forms of macro substitution: 1. Simple macro substitution.

What are preprocessor macros?

The C preprocessor is a macro preprocessor (allows you to define macros) that transforms your program before it is compiled. These transformations can be the inclusion of header file, macro expansions etc. All preprocessing directives begin with a # symbol. For example, #define PI 3.14.

What is a #include preprocessor?

In C and C++, the #include preprocessor directive causes the compiler to replace that line with the entire text of the contents of the named source file (if included in quotes: “”) or named header (if included in angle brackets: <>); note that a header doesn’t need to be a source file.

What is preprocessor operator C?

Four preprocessor-specific operators are used in the context of the #define directive. The stringizing, charizing, and token-pasting operators are discussed in the next three sections. For information on the defined operator, see The #if, #elif, #else, and #endif directives.

What is C++ 2a?

C++20/C++2a brings new features to the synchronization library, including atomic smart pointers, latchers, and barriers. We review its all-new coroutines (a major concept found in other leading programming languages that simplifies writing code for parallel execution).

Can a macro parameter be replaced in a string?

Parameters are not replaced inside string constants, but you can use the ‘#’ preprocessing operator instead. When a macro parameter is used with a leading ‘#’, the preprocessor replaces it with the literal text of the actual argument, converted to a string constant.

How to convert a macro to a string?

Sometimes you may want to convert a macro argument into a string constant. Parameters are not replaced inside string constants, but you can use the ‘ # ’ preprocessing operator instead. When a macro parameter is used with a leading ‘ # ’, the preprocessor replaces it with the literal text of the actual argument, converted to a string constant.

What is the definition of a preprocessor macro?

Introduce a definition for a preprocessor macro named macro , invocations of which are replaced by the tokens given in replacement-list. The first form of this command defines an “object-like” macro, which takes no arguments; the second form defines a “function-like” macro, which takes the arguments given in arglist .

How does the preprocessor stringize a string in C?

Stringizing in C involves more than putting double-quote characters around the fragment. The preprocessor backslash-escapes the quotes surrounding embedded string constants, and all backslashes within string and character constants, in order to get a valid C string constant with the proper contents.