Question

Part II: gdb (Debugging under Unix)

1. create a new directory named by Inlab6Part2
2. enter the directory Inlab6Part2
3. create a file named by reverse_new.c with the following contents:

/*reverse.c */

#include <stdio.h>

void reverse(char *before, char *after);

main()

{

      char str[100];    /*Buffer to hold reversed string */

      reverse("cat", str); /*Reverse the string "cat" */

      printf("reverse(\"cat\")=%s\n", str); /*Display result */

      reverse("noon", str); /*Reverse the string "noon" */

      printf("reverse(\"noon\")=%s\n", str); /*Display result */

     

}

void reverse(char *before, char *after)

{

      int i;

      int j;

      int len;

      len=strlen(before);

      for(j=len, i=0; j>=0; j--, i++)

                  after[i]=before[j];

      after[len]=NULL;

}

4. See the output, is it right?
5. compile reverse_new.c and prepare the debugger information at the same time.(To debug a program, it must have been compiled using the –g option to gcc, which places debugging information into the object module.)
6. Now you start the debugger and fix the errors.
   1. set breakpoint in line 1 and then go through step by step, print the value of arguments after each step.
   2. make sure you use most of the commands in the handout, and then print everything you did(all the commands and outputs).

Answer 1

The program after removing the errors is below:

#include <stdio.h>

void reverse(char *before, char *after);

void main()

{

      char str[100];    /*Buffer to hold reversed string */

      reverse("cat", str); /*Reverse the string "cat" */

      printf("reverse(\"cat\")=%s\n", str); /*Display result */

      reverse("noon", str); /*Reverse the string "noon" */

      printf("reverse(\"noon\")=%s\n", str); /*Display result */

     

}

void reverse(char *before, char *after)

{

      int i;

      int j;

      int len;

      len=strlen(before);

      for(j=len-1, i=0; j>=0; j--, i++)

                  after[i]=before[j];

      after[len]=NULL;

}

The only change in the code is that 'j' variable inside for loop of reverse() is initialized to len-1 instead of len;

The debug console screen is as below: