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A macro is a fragment of code that is given a name. You can define a macro in C using the #define preprocessor directive. Here's an example. Here, when we use c in our program, it is replaced with 299792458 .
In C, the macro is used to define any constant value or any variable with its value in the entire program that will be replaced by this macro name, where macro contains the set of code that will be called when the macro name is used in the program.
12) What is the output of C program with macros.? Explanation: Inside main the statment printf("Error=%d",10) is substituted. printf("Error=%d",10);
The macro in C language is known as the piece of code which can be replaced by the macro value. The macro is defined with the help of #define preprocessor directive and the macro doesn't end with a semicolon(;). Macro is just a name given to certain values or expressions it doesn't point to any memory location.
The problem is that when you have a macro replacement, the preprocessor will only expand the macros recursively if neither the stringizing operator # nor the token-pasting operator ## are applied to it. So, you have to use some extra layers of indirection, you can use the token-pasting operator with a recursively expanded argument:
#define TOKENPASTE(x, y) x ## y
#define TOKENPASTE2(x, y) TOKENPASTE(x, y)
#define UNIQUE static void TOKENPASTE2(Unique_, __LINE__)(void) {}
Then, __LINE__ gets expanded to the line number during the expansion of UNIQUE (since it's not involved with either # or ##), and then the token pasting happens during the expansion of TOKENPASTE.
It should also be noted that there is also the __COUNTER__ macro, which expands to a new integer each time it is evaluated, in case you need to have multiple instantiations of the UNIQUE macro on the same line. Note: __COUNTER__ is supported by MS Visual Studio, GCC (since V4.3), and Clang, but is not standard C.
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