breakpoint

A breakpoint is a deliberate stopping point in a program's execution used to inspect state and control flow during debugging. Breakpoints are managed by a debugger and can be unconditional or conditional on a boolean expression, a variable value, or a hit count. When execution reaches a breakpoint, the program pauses, allowing the developer to inspect memory, variables, the call stack, and register state, and to decide how to continue.

There are several kinds of breakpoints. Software breakpoints temporarily modify the program's code, typically by inserting a trap instruction; hardware breakpoints use processor debug facilities without altering code and are useful when code modification is not possible. Breakpoints can be set at particular lines (line breakpoints), at function entry, or on specific data values (watchpoints). Conditional breakpoints evaluate an expression at hit time; logpoints record events without stopping; and temporary breakpoints disappear after being hit.

Implementation details: In x86, software breakpoints commonly use the INT 3 instruction (0xCC). In ARM, a BKPT instruction is used. Debugger interfaces in managed runtimes provide breakpoint capabilities through high-level APIs (e.g., JDWP for Java, CLR debugging). Breakpoints may be affected by optimizations and often are disabled in release builds. Modern debuggers also support features like stepping (into, over, out), break on exceptions, and remote debugging.

Beyond debugging, the term breakpoint appears in other fields. In responsive design, a breakpoint is a screen size threshold at which layout changes. In mathematics and data analysis, a breakpoint can denote a point where a function or series changes its behavior or segmentation occurs.