C Debugging in Visual Studio and emacs Weve

C++ Debugging (in Visual Studio and emacs) • We’ve looked at programs from a text-based mode – – Shell commands and command lines Text editors, compiler, linker How the program receives input and generates output General program structure and logic • We’ve also looked at Visual Studio – In which all of these functions are integrated… – …within a nice graphical environment • Today we’ll bring those perspectives together – Debug a simple example program in Visual Studio – Look at how do the same thing within emacs CSE 232: C++ debugging in Visual Studio and emacs

Getting Started • To set up your own environment for what we’ll cover – Log on and then ssh into grid. cec. wustl. edu – Create a new directory (e. g. , mkdir prefix_adder) – Save files from course web page (or copy them from the ~cse 232/. www-docs/ directory) into that directory: Makefile prefix_adder. h prefix_adder. cc • Also download those files to your Windows desktop – Create a new project in Visual Studio – Copy those files into the new project in Visual Studio – Build the project CSE 232: C++ debugging in Visual Studio and emacs

Debugging an Example Program • Now we’ll use Visual Studio to debug a program – Step through (and into) functions – Watching the call stack and variable values • But, before we start using Visual Studio… – – What are we trying to achieve? What do we expect our program to do? How might our program fail? Can we make predictions and test them? • Thinking: the most powerful way to debug – Scientific method should guide what you do • hypothesis, prediction, experiment, analysis – Tools can help you follow this disciplined approach faster CSE 232: C++ debugging in Visual Studio and emacs

What the Example Program Does • Called with command line arguments. /prefix_adder + 8 + 9 10 • Calculates prefix addition expressions + 8 + 9 10 + + 8 9 10 • These are equivalent to their infix versions (8 + (9 + 10)) ((8 + 9) + 10) • Key idea: walk through expresion, calculate value same result 1 2 8 + 4 9 3 + different order 5 10 3 8 1 + 2 + 4 9 CSE 232: C++ debugging in Visual Studio and emacs 5 10

How the Example Program Can Fail • Too few arguments in expression. /prefix_adder + 8 + 9 • Cannot calculate result + 8 + 9 (needs another value to finish 2 nd + operation) 1 2 8 + 4 9 3 + ? ? ? • Exercise: try this on your own, for practice CSE 232: C++ debugging in Visual Studio and emacs

Example Program: Header File // prefix_adder. h // // author: Chris Gill cdgill@cse. wustl. edu // // purpose: Declarations for a simple prefix adder program, which // takes the command line arguments as a prefix addition // expression and computes an integer result. #ifndef PREFIX_ADDER_H #define PREFIX_ADDER_H // Function prototypes. void usage (char * program_name); int parse_and_compute (int & current_index, int last_index, char *argv[]); #endif /* PREFIX_ADDER_H */ CSE 232: C++ debugging in Visual Studio and emacs

Example Program: Start of the Source File // prefix_adder. cc // // author: Chris Gill cdgill@cse. wustl. edu // // purpose: definitions for a simple prefix adder program, which // takes the command line arguments as a prefix addition // expression and computes an integer result. #include "prefix_adder. h" #include <iostream> <string> <sstream> <cstring> // // For For std output stream and manipulators. standard C++ strings. standard string streams. C-style string functions // Helper function to print out the program's usage message. void usage (char * program_name) { cout << "Usage: " << program_name << " <argument> [<argument>]. . . " << endl << "Purpose: computes program arguments as prefix addition expression" << endl; } CSE 232: C++ debugging in Visual Studio and emacs

Example Program: Main Function int main (int argc, char *argv[]) { // A few useful constants for argument positions const int minimum_arguments = 2; const int starting_index = 1; const int program_name_index = 0; if (argc < minimum_arguments || strcmp (argv[starting_index], "--help") == 0) { usage (argv[program_name_index]); return 1; } try { // Pass the current and last index to use, and the array, to the // expression parsing function, and store the result. int current_position = starting_index; int value = parse_and_compute (current_position, argc - 1, argv); // Print out the result, and return success value. cout << "The value calculated is " << value << endl; return 0; } catch (. . . ) { cout << "caught exception" << endl; return -1; } } CSE 232: C++ debugging in Visual Studio and emacs

Example Program: Parsing Function // Helper function to parse the input symbols and compute a value. int parse_and_compute (int & current_index, int last_index, char *argv[]) { // make sure we're still in the argument range if (current_index > last_index) { throw; } // look for a single-symbol addition operator if (strlen (argv[current_index]) == 1 && *(argv[current_index]) == '+') { int first_operand = parse_and_compute ( ++current_index, last_index, argv); int second_operand = parse_and_compute (current_index, last_index, argv); return first_operand + second_operand; • Exercise: } // treat anything else as an integer else { int result; istringstream i (argv[ current_index++]); i >> result; return result; } } – Set a break point at the first if statement in this function – Watch how stack grows/shrinks if you have debug continue CSE 232: C++ debugging in Visual Studio and emacs

Debugging in emacs CSE 232: C++ debugging in Visual Studio and emacs

Open Makefile, Source, Header Files in emacs CSE 232: C++ debugging in Visual Studio and emacs

Compile the Program: Esc x compile CSE 232: C++ debugging in Visual Studio and emacs

Hit Enter to Run “make -k” CSE 232: C++ debugging in Visual Studio and emacs

Compilation Succeeded CSE 232: C++ debugging in Visual Studio and emacs

Launch Debugger: Esc x gdb CSE 232: C++ debugging in Visual Studio and emacs

Run “gdb prefix_adder” CSE 232: C++ debugging in Visual Studio and emacs

GDB Debugging Prompt CSE 232: C++ debugging in Visual Studio and emacs

Setting Breakpoints CSE 232: C++ debugging in Visual Studio and emacs

Running With Command Line Arguments CSE 232: C++ debugging in Visual Studio and emacs

At Breakpoint in Main CSE 232: C++ debugging in Visual Studio and emacs

Stepping Through the Program CSE 232: C++ debugging in Visual Studio and emacs

What Options Does Emacs/GUD Provide? CSE 232: C++ debugging in Visual Studio and emacs

Stepped into Function Call, now at a Breakpoint CSE 232: C++ debugging in Visual Studio and emacs

Printing out Values of Variables CSE 232: C++ debugging in Visual Studio and emacs

Continue to next Breakpoint, Look at Stack CSE 232: C++ debugging in Visual Studio and emacs

Exercise • Build and debug a damaged version of the program – Save another file from course web page into the project (or create a new project with same Makefile and header file) bad_prefix_adder. cc – Build the new version of the program • Debug what’s wrong with the program (no fair using diff to detect code differences ; -) – Run the program with different inputs – Observe what happens (how does it go wrong? ) – Trace through the program in Visual Studio to narrow down the possible cause(s) of the problem(s) • If you’d like to, also try the same thing in emacs – Fix the error(s), rebuild, and re-run to observe its behavior CSE 232: C++ debugging in Visual Studio and emacs