Description
Lab goals: C primer, pointers to data, structures, and pointers to functions.
(This lab is to be done SOLO)
Task 0: Using gdb(1) to debug segmentation fault
You should finish this task before attending the lab session.
gdb(1), the GNU Debugger, is a powerful tool for program debugging and inspection. When a program is compiled for debugging and run inside gdb, the exact location of segmentation fault can be determined. In addition, the state of the processor registers and values of the variables at the time of the fault can be examined.
1. Write a Makefile for the program.
2. Specify compilation flags appropriate for debugging using gdb. 3. Find the location and the cause of the segmentation fault using gdb.
4. Fix the bug and make sure the program works correctly.
5. By the end of this task you should be familiar with the following GDB features : Breakpoints, Watchpoints, Source listing, Stepping, and Printing variables and memory
The tasks below are to be done only during the lab session!
Task 1: Extend toy_printf function
The function printf() and its cousins are among of the most versatile and well-known functions for sending formatted strings as output to files and the screen. They are implemented by many languages, including C, Java, Perl, PHP, Python, Ruby, and a handful of others.
One of printf()’s signature benefits is its ability to accept a variable number of arguments. This allows printed text to contain countless variations of formatted values and strings. In this task, you will learn how to extend this functionality to create your own printf() wrapper function. The source code you need to modify in this lab is provided in the files toy_printf.c, main[1].c, toy_stdio.h
toy_printf’s manual
Synopsis
#include “toy_stdio.h”
int toy_printf(char* format, …);
Description
toy printf outputs to stdout according to the given null-terminated format string
(see below) and returns the number of characters written.
(after format) of its related argument.
Format flags
A format flag is a percent (‘%’) sign followed by one of the following format identifiers. In the output, the format flag is replaced with string representing its related argument.
identifiers:
d signed integer as a decimal number u unsigned integer as a decimal number b unsigned integer as a binary number o unsigned integer as a octal number x unsigned integer as a hexadecimal number. Letter numerals printed in lower case X unsigned integer as a hexadecimal number. Letter numerals printed in upper case s null-terminated string c character according to the ascii table % the ‘%’ character.
Task 1a:Print unsinged
Fix the output for integers of numbers in bases other than base 10, so that the numbers are printed as unsigned rather than signed. For example:
toy_printf(“Hex unsigned: %x “, -1); toy_printf(“Octal unsigned: %o “, -1);
Output:
#> main
Hex unsigned: ffffffff Octal unsigned: 37777777777
#>
T1b- Print unsigned integers
Add support for printing unsigned integers %u (“int” argument is output as an unsigned decimal integer). For example:
toy_printf(“Unsigned value: %u “, 15); toy_printf(“Unsigned value: %u “, -15);
Output:
#> main
Unsigned value: 15
Unsigned value: 4294967281
#>
T1c – Printing arrays
Add support for %Ad, %As, %Ax, etc., to print arrays of integers, string, hexadecimal integers, etc. The size of the array is passed as an argument. For example:
int integers_array[] = {1,2,3,4,5};
char * strings_array[] = {“This”, “is”, “array”, “of”, “strings”}; int array_size = 5;
toy_printf(“Print array of integers: %Ad “, integers_array, array_size); toy_printf(“Print array of strings: %As “, strings_array, array_size);
Output:
#> main
Print array of integers: {1, 2, 3, 4, 5}
Print array of strings: {This, is, array, of, strings} #>
T1d – The Width Field
For example:
toy_printf(“Non-padded string: %s “, “str”); toy_printf(“Right-padded string: %6s “, “str”); toy_printf(“Left-added string: %-6s “, “str”);
Output:
#> main
Non-padded string: str
Right-padded string: str #
Left-padded string: str
#>
toy_printf(“With numeric placeholders: %05d “, -1);
Output:
#> main
With numeric placeholders: -0001
#>
Deliverables:
You must submit source files in respective folders, and also a makefile that compiles them. The source files must be organized in the following tree structure (where ‘+’ represents a folder and ‘-‘ represents a file):
+ task1d
– makefile
– toy_printf.c
– main.c
– toy_stdio.h
Note that the folder name “task1d” should be used, regardless of whether you completed task1d or not.
Submission instructions
Create a zip file with the relevant files (only).
Upload zip file to the submission system.
Download the zip file from the submission system and extract its content to an empty folder.
Compile and test the code to make sure that it still works.
