CODEWITHSUNDEEP
c
user3016320
user3016320

Reputation: 59

Concatenation of two definition

#define ID  proj1

#define PROJ ID##_data.h

As per my requirements definition of PROJ should have proj1_data.h

When I print PROJ It should give proj1_data.h ,

Please help me to get the desired result. Thanks in advance !

Upvotes: 0

Views: 171

Answers (1)

jxh
jxh

Reputation: 70472

You can only print a string. So to print PROJ, you would need to turn it into a string.

#define STRINGIZE(X) #X
#define STRINGIZE2(X) STRINGIZE(X)

STRINGIZE applies the stringizing operator on the argument. It turns the argument into a string, essentially by surrounding it with quotation marks, and escaping the contents as necessary to create a valid string. STRINGIZE2 is used to allow the argument to be expanded by the preprocessor before it is turned into a string. This is useful when you want to stringize the expansion of a macro instead of the macro itself. For example STRINGIZE2(__LINE__) will result in a string that represents the current line in the file, e.g. "1723". However, STRINGIZE(__LINE__) results in the string "__LINE__".

Your definition of PROJ faces a similar issue. It actually results in the token ID_data..h rather than proj1_data.h. You need a level of expansion indirection to allow ID to expand before you concatenate.

#define PASTE(X, Y) X ## Y
#define MKFILE(X) PASTE(X, _data.h)
#define PROJ STINGIZE2(MKFILE(ID))

Using STRINGIZE2 allows the MKFILE invocation to expand. Allowing MKFILE to invoke PASTE allows the ID token to expand.

Upvotes: 2

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