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Language in C Interview Questions and Answers

Question: On including a file twice I get errors reporting redefinition of function.
How can I avoid duplicate inclusion?
Answer: Redefinition errors can be avoided by using the following macro definition. Include this definition in the header file.
#if !defined filename_h
#define filename_h
/* function definitions */
#endif
Replace filename_h with the actual header file name. For example, if name of file to be included is 'goto.h' then replace filename_h with 'goto_h'.

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