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Asked: 2026-06-11T09:58:43+00:00

I was wondering if there was a way in C language to define #define

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I was wondering if there was a way in C language to define #define like this:

#define something #define
something a 42
something b 42
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  1. Editorial Team

    No, there isn’t. If the expansion of a macro generates something that looks like a preprocessor directive, it is not processed as one, leaving a # in the source code that is seen by the compiler proper, which will then object that the # is an unexpected token (syntax error).

    ISO/IEC 9899:2011

    6.10.3.4 Rescanning and further replacement

    ¶3 The resulting completely macro-replaced preprocessing token sequence is not processed
    as a preprocessing directive even if it resembles one, but all pragma unary operator
    expressions within it are then processed as specified in 6.10.9 below.

    The ‘pragma unary operator’ referred to is the _Pragma() operator which takes a string literal.

    The wording in C99 is very similar, and the wording is C89 is similar but doesn’t mention the _Pragma operator because it didn’t exist in C89.

    You can find drafts of the C2011 standard at the Open Standard web site:

    along with working papers, ‘mailings’ for the committee meetings, etc.

    (JTC1 is Joint Technical Committee 1; SC22 is Standardization Committee 22 for programming languages; WG14 is Working Group 14, responsible for the C standard. WG21 is responsible for the C++ standard.)

    You can obtain your own, personalized copy of the PDF of the standard from ANSI for 30 USD. I regard that as a necessary investment for any serious C programmer.

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