'A' sues 'B' for rent. 'B' contends that 'C' and not 'A' is the landlord. A fails to prove his title…

Section 11 CPC bars only a matter directly and substantially in issue in a former suit between the same parties, or parties claiming under them. C was not a party to the rent suit, and that suit decided only whether A could recover rent from B, so the later suit for a declaration of title against B and C is not barred: "The suit is not barred as the parties in both the suits are not the same". The similarity or difference of the relief claimed is not the test.