Why is #define int long acceptable by C++ compiler?

Asked May 15 '22 at 07:42

Active May 15 '22 at 07:43

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I thought C++ lines like

#define int long long

would be reported as error by C++ compiler, because I think since the directive #define is used for text replacing and we should not permit a keyword to be replaced to avoid chaos.

But I tested gcc will compile with no error. Is there any reason or goodness to keep this as acceptable?

edited May 15 '22 at 07:43

asked May 15 '22 at 07:42

Wason

The behaviour is undefined (according to the C++ standard). But as a matter of pragmatism, it'd be bad if compilers objected unconditionally: https://stackoverflow.com/q/72177535/817643 – StoryTeller - Unslander Monica May 15 '22 at 07:44
Technically the compiler parses the output of the preprocessor, so it has no chance to detect any preprocessor directive – MatG May 15 '22 at 11:01
@MatG Cool reply. – Wason May 19 '22 at 08:25

Why is #define int long acceptable by C++ compiler?

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