It is possible that there are limits in gdb (the IDE uses gdb as debugger).
I dont know if/where this is documented for gdb.
This may also depend on your hardware / your CPU.
There are 2 ways to do watchpoints
1) hardware watch points. those are a feature of your CPU. And the number of those is limited by your CPU.
2) Software watchpoints. (if supported by gdb for your platform / and not sure if the IDE even tells gdb to try them)
Software watchpoints are really slow. It basically means to single step the app, and check the memory after each step. This would really slow down execution of your app.
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In any case, if the breakpoint can not be set, there should be an error, and you should get the option to continue without that breakpoint.
But I haven't tested that, and I don't know what gdb will report in this case.