c - Concatenation of two definition -

#define id  proj1  #define proj id##_data.h 

as per requirements definition of proj should have proj1_data.h

when print proj should give proj1_data.h ,

please me desired result. in advance !

you can print string. print proj, need turn string.

#define stringize(x) #x #define stringize2(x) stringize(x) 

stringize applies stringizing operator on argument. turns argument string, surrounding quotation marks, , escaping contents necessary create valid string. stringize2 used allow argument expanded preprocessor before turned string. useful when want stringize expansion of macro instead of macro itself. example stringize2(__line__) result in string represents current line in file, e.g. "1723". however, stringize(__line__) results in string "__line__".

your definition of proj faces similar issue. results in token id_data..h rather proj1_data.h. need level of expansion indirection allow id expand before concatenate.

#define paste(x, y) x ## y #define mkfile(x) paste(x, _data.h) #define proj stingize2(mkfile(id)) 

using stringize2 allows mkfile invocation expand. allowing mkfile invoke paste allows id token expand.