Is a police officer required to inform a person to be arrested of the cause of their arrest?

In People v. Herman, 163 Cal.App.2d 821, 329 P.2d 989, it was held that under section 841 of the Penal Code it is not necessary for the officer to inform the person to be arrested of the cause of his arrest when the person making the arrest has reasonable cause to believe that the person to be arrested is actually engaged in the commission of an offense.

In Willson v. Superior Court, 46 Cal.2d 291, 294 P.2d 36, it was held where it may be inferred from the fact that petitioner was arrested in a public bar, but made no outcry or objection, that she realized that the arresting officer was a police officer whose purpose was to make an arrest, it is immaterial that petitioner was not expressly informed of the officer's authority and purpose.