René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Function-like macro not expanded a second time in some cases","articleBody":"Preprocessing of this code with simplecpp:\r\n```cpp\r\n#define CAT(a, b) CAT2(a, b)\r\n#define CAT2(a, b) a ## b\r\n#define FOO x\r\n#define BAR() CAT(F, OO)\r\n#define BAZ CAT(B, AR)()\r\nBAZ\r\n```\r\nproduces this result:\r\n```\r\nCAT ( F , OO )\r\n```\r\nAll mainstream preprocessors (GCC, Clang, MSVC) produce this result (https://godbolt.org/z/9GhhTarE3):\r\n```\r\nx\r\n```\r\n\r\nIt seems that simplecpp decides to not expand `CAT` a second time during evaluation of `BAZ`. I don't know if this is correct from the point of view of the standard.\r\n\r\nSome additional observations:\r\n1. If the last line is replaced with `CAT(B, AR)()` then all preprocessors produce the same result: `x`.\r\n2. If `BAR()` is converted from function-like macro to regular macro:\r\n    ```cpp\r\n    #define BAR CAT(F, OO)\r\n    #define BAZ CAT(B, AR)\r\n    ```\r\n    then all preprocessors produce the same result: `CAT ( F , OO )`.\r\n","author":{"url":"https://github.com/dummyunit","@type":"Person","name":"dummyunit"},"datePublished":"2022-01-18T21:55:13.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/231/simplecpp/issues/231"}