Back to DFS's C Page

This brief description of how to use gdb will assume that you are tracing through the following program which has been saved as tri.c.

/* tri.c
   DFStermole
   28 September 98
   Purpose: Calc the area of a triangle
*/

#include <stdio.h>      /* standard I/O header file */

void main()
{
   int b;    /* base */
   int h;    /* height */
   float A;  /* Area */

   /* -------------------Introduction------------------ */
   printf("This program calculates the area of a triangle\n");
   printf("after you enter its dimensions.\n");
   printf("When asked to, type in a dimension and hit the ENTER key.\n");
   printf("\n");
   /* -------------------Inputting Data------------------*/
   printf("What is the length of the triangle's base? ");
   scanf("%d", &b);
   printf("What is the triangle's height? ");
   scanf("%d", &h);
   /* -------------------Calculation------------------ */
   A = b * h / 2.0;
   /* -------------------Printing Results------------------ */
   printf("\n");
   printf("The area of a triangle with a base of %d units and\n", b);
   printf("a height of %d units is %.1f square units.\n", h, A);
}

Getting Ready

1. Compile the program including debugging info.
   gcc -g -o tri tri.c
2. Run gdb, loading the program tri.
   gdb tri

Some gdb Commands

• l
  "L"ist source from last line printed.
• l nn
  "L"ist source line nn with context.
• b nn
  Set a "B"reakpoint at line nn.
• r
  "R"un the program to a breakpoint or to the end.
• c
  "C"ontinue running program.
• n
  Continue to "N"ext line of code, not entering functions.
• n nn
  Continue through "N"ext nn lines of code, not entering functions.
• s
  "S"tep through one line of code, entering functions.
• s nn
  "S"tep through nn lines of code, entering functions.
• p varname
  "P"rint the value of varname.
• p/x varname
  "P"rint the value of varname in hexadecimal.
• p &varname
  "P"rint the address of varname in hexadecimal.
• help
  Print the help info.
• q
  "Q"uit gdb.
• ENTER
  Repeat the most recent command.

Using .gdbinit

The .gdbinit file is automatically executed when gdb is run. Create a .gdbinit file with the following lines and then run gdb.

b 16
r