If the file to be included doesn't exist, the preprocessor flashes an error message.

More Questions from C Preprocessor

• Preprocessor directive #undef can be used only on a macro that has been #define earlier
• Once preprocessing is over and the program is sent for the compilation the macros are removed from the expanded source code.
• Every C program will contain at least one preprocessor directive.
• A header file contains macros, structure declaration and function prototypes.
• In a macro call the control is passed to the macro.
• A preprocessor directive is a message from compiler to a linker.
• A macro must always be defined in capital letters.
• Macros with arguments are allowed
• Macros have a local scope.
• There exists a way to prevent the same file from getting #included twice in the same program.

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