Debuggers

A debugger is a tool that lets you walk through the execution of a program to identify and resolve bugs.

Why

• Lets me go through a program step by step
  • I don't have to write print statements in a long program where I am unsure about what I want to achieve
• Depending on the debugger, I can go back in time (the debugger in this case keeps track of all changes a program makes so they can be reverted) to replay a step in a program.

Examples

• gdb (for C and C-based programs)
• Pdb (for Python)
  • Pdb is a hybrid of a debugger and a programming environment. You can run valid Python code in Pdb.

Features

• Step back to a previous line of code
• Step forward to the next line of code
• Change the value of a variable (Pdb)
• See the Assembly calls behind a line of code (gdb)

Usage Notes

• A blank line (created when you click Enter) runs the same command as the one you last executed
• Set a breakpoint where the program will stop
• In the case of Pdb, import the library on the line where I want the interactive prompt to come up

See Also

• Program Introspection talk on Missing Semester
• Profilers