In what circumstances will a search of a defendant's clothing result in an illegal search?

In People v. Martines, 228 Cal.App.2d 245, 39 Cal.Rptr. 526, an officer made a superficial search of the outside of the defendant's clothing and felt a hard object like a knife; he could not feel a blade; the object was about three inches long; the officer then put his hand in the pocket and pulled out what felt like a wad of paper consisting of nine marijuana cigarettes; the knife was then removed. That was held to be an illegal search.