How often was it that sieges ended in starvation/surrender?

[Jorsalfar]

I believe there were customary laws of warfare that governed how sieges were to be conducted. During the 2nd English Civil War the Royalists refused to surrender Colchester in a militarily hopeless position. When the town surrendered after two and a half months the senior commanders were refused quarter and executed for causing unnecessary suffering by prolonging the siege.

This! A defender was expected to ask for terms when the situation clearly was impossible. If the defenders for some reason did not do that they would usually not be given quarter.

 

[BaronNoir]

The said impossibility was usually a breach in the fortifications.

Capitulating after a breach was generally seen as honourable, capitulating before cowardly.

 

[Jorsalfar]

The said impossibility was usually a breach in the fortifications.

Capitulating after a breach was generally seen as honourable, capitulating before cowardly.

Not necessarily, "impossible" could also mean cut off from supplies and no realistic hope to be relieved.

 

[BaronNoir]

At least under Louis XIII and Louis XIV, fortresses were duly excepted to hold until the breach was made. (of course, they usually capitulated because of supply issue)