[treeplayer] Support left-justified columns in TTree::Scan - #22951
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TTreePlayer::Scan documents that the "col=" format strings follow the printf specification, but the parser did not accept the '-' left-justification flag: the scan of the "col=" value stopped at the first '-', so every column from there on silently reverted to the default (right-justified) width. Accept '-' while scanning the "col=" value, read the per-column size as a signed integer (a negative size now marks a left-justified column), and build the field-width format strings so a negative width stays valid printf: the sign drives the justification while std::abs() is used for the precision and the '*' border widths. Closes root-project#11786. 🤖 Done with the help of AI.
dpiparo
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Jul 29, 2026
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Thanks for addressing this long standing issue!
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TTreePlayer::Scan documents that the "col=" format strings follow the printf specification, but the parser did not accept the '-' left-justification flag: the scan of the "col=" value stopped at the first '-', so every column from there on silently reverted to the default (right-justified) width.
Accept '-' while scanning the "col=" value, read the per-column size as a signed integer (a negative size now marks a left-justified column), and build the field-width format strings so a negative width stays valid printf: the sign drives the justification while std::abs() is used for the precision and the '*' border widths.
Closes #11786.
🤖 Done with the help of AI.