CODEWITHSUNDEEP
cc-preprocessorpreprocessor
sergej
sergej

Reputation: 18009

Pre-processor: Expand a macro only once

Is it possible to have a macro expanded only once? In the following example, MYCONCAT is expanded to func_1(10). I want it to expand to func_BAR(10).

#define BAR 1  // included from a file I cannot change
#define FOO BAR

#define MYCONCAT2(c) func_ ## c
#define MYCONCAT(c, x) MYCONCAT2(c)(x)

MYCONCAT(FOO, 10) // is 'func_1(10)', but I want it to be 'func_BAR(10)'

Upvotes: 0

Views: 260

Answers (3)

sergej
sergej

Reputation: 18009

Simply change #define BAR to #define _BAR and and remove the _ from func.

#define BAR 1  // included from a file I cannot change
#define FOO _BAR

#define MYCONCAT2(c) func ## c
#define MYCONCAT(c, x) MYCONCAT2(c)(x)

MYCONCAT(FOO, 10) // 'func_BAR(10)'

Upvotes: 2

Eric Postpischil
Eric Postpischil

Reputation: 224002

Include the file that defines BAR only after the last place where MYCONCAT is used (with something that expands to BAR) instead of before it.

Upvotes: 2

KamilCuk
KamilCuk

Reputation: 141748

Is it possible to have a macro expanded only once?

No, it is not possible to partially expand a macro.

Upvotes: 2

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