How do breakpoints work in C++ code?

Question

How do breakpoints work in C++ code? Are they special instructions inserted in between some assembler instructions when the code is compiled? Or is there something else in p

Answer 1

According to this blog entry on technochakra.com you are correct:

Software breakpoints work by inserting a special instruction in the program being debugged. This special instruction on the Intel platform is “int 3″. When executed it calls the debugger’s exception handler.

I'm not sure how stepping into or over the next instruction is implemented though. However, the article goes on to add:

For practical reasons, it is unwise to ask for a recompilation whenever a breakpoint is added or deleted. Debuggers change the loaded image of the executable in memory and insert the “int 3″ instruction at runtime.

However, this would only be used for the "run to current line option".