http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58687
Bug ID: 58687 Summary: "#line __LINE__ ..." changes subsequent line numbers Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: preprocessor Assignee: unassigned at gcc dot gnu.org Reporter: mtewoodbury at gmail dot com A preprocessor directive of the form '#line __LINE__ ..." should NOT change the line number. That is '__LINE__' should evaluate to the number of the NEXT line in this context. If you read the standards carefully, __LINE__ should have a value equal to the number of 'new line' characters seen by the phaee 1 translation plus one WHEN THE SUBSTITUTION OCCURS (unless modified by previous #line directives). When the subsituyion occurs is controlled by the parsing done in phase 4 of translation. Specifically, subsitution in preprocessing directives occure when the specific form of the directive has been formally identified AND that form calls for <pp_token> aubstitution. The form in this case is: '#' 'line' <pp_token>+ <new_line> Note that the terminating <new line> token has to have been seen BEFORE the form is identifiad. That means __LINE__ will normally have the line number of the NEXT line in the file when the substitution occurs. FURTHER NOTE that any <new line> tokens in comments will also have been counted when the substiturion occurs. What is apparently happening instead is that the substitution is being made BEFORE the particular form of the '#line' directive has been completely and formally identified. In other wordds you have folded the translation phases togeather and botched up the carefully structured procedure with its intentional delays in substitution set forth in the standard.