Debugging

Before we get acquainted with the debugging possibilities, let's write a short program to find the sum of numbers: suma.c

Summing Numbers

Initialize a variable sum=0. Print the value of argc. Print the values in argv. The numbers counter num_count is the second value in argv. Read a number from the keyboard num_count times and add it to the sum. Print the value of the obtained sum.

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char* argv[]) 
{
  int numbers_count = 0, sum = 0;
  char temp_str[50];
  printf("The value of argc: %d\n", argc);
  printf("The value(s) in argv:\n");
  for(int i = 0; i < argc; i++) {
    printf("> argv[%d]=%s\n", i, argv[i]);
  }
  numbers_count = atoi(argv[1]);
  printf("Enter %d numbers:\n", numbers_count);
  for(int i = 0; i < numbers_count; i++) {
    scanf("%s", temp_str);
    sum += atoi(temp_str);
  }
  printf("Total sum is %d\n", sum);
}

12_suma.png

Debugging

To compile the source code of the program with debugging enabled:

gcc suma.c -о suma

To start the debugger:

gdb suma

To set a breakpoint where the program will stop execution:

b [function name, line number]

To start the program:

r [command line arguments]

The table provides the shortcut key combinations useful when working with the debugger:

Key	Information
h	Help
n	Step forward one block of code
s	Step forward one line of code
p [variable]	Prints the value of the variable variable
info locals	Prints the values of all local variables
bt	Shows the sequence of functions called up to this execution point
q	Exit

Reference: Introduction to GDB и Harvard University CS50