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#define BINARY_TREE_PARENT_CORRECT(son, parent) ((son) ? (son->parent == parent) : 1)

It turns out that the parent in son->parent which means a struct member will also be replaced by the parent in son, parent.

The gcc version is 4.1.2.

Do you think it's a bug or expected behavior?

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3 Answers 3

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The behavior is correct. All unquoted occurrences of parent are substituted. The preprocessor does not try to guess what you mean. It just replaces what you say.

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This is expected behavior. The preprocessor does not know C's syntax (except when evaluating the controlling expression in an #if) -- it just replaces tokens.

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Easy fix: Change the parameter name to be different from your element name.

#define BINARY_TREE_PARENT_CORRECT(son, par) ((son) ? (son->parent == par) : 1)

cpp won't match par against parent, so you'll get the behaviour you expect.

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