C - Custom printf function

Background Context

Custom printf function

Requirements

General

• Used editors: vi, vim
• All files will compiled on Ubuntu 20.04 LTS using gcc, using the options -Wall -Werror -Wextra -pedantic -std=gnu89
• All files end with a new line
• Code for custom printf uses the Betty style. Checked using betty-style.pl and betty-doc.pl
• No global variables used
• No more than 5 functions per file
• The prototypes of all your functions are included in header file called main.h
• All header files are include guarded

More Info

Global functions and macros used

• write (man 2 write)
• malloc (man 3 malloc)
• free (man 3 free)
• va_start (man 3 va_start)
• va_end (man 3 va_end)
• va_copy (man 3 va_copy)
• va_arg (man 3 va_arg)

Compilation

$ gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c

Tasks

task0

Write a function that produces output according to a format.

• Prototype: int _printf(const char *format, ...);
• Returns: the number of characters printed (excluding the null byte used to end output to strings)
• write output to stdout, the standard output stream
• format is a character string. The format string is composed of zero or more directives. See man 3 printf for more detail. You need to handle the following conversion specifiers:
  • c
  • s
  • %
• You don’t have to reproduce the buffer handling of the C library printf function
• You don’t have to handle the flag characters
• You don’t have to handle field width
• You don’t have to handle precision
• You don’t have to handle the length modifiers

task1

Handle the following conversion specifiers:

• d

• i

• You don’t have to handle the flag characters

• You don’t have to handle field width

• You don’t have to handle precision

• You don’t have to handle the length modifiers

task2

Handle the following custom conversion specifiers:

• b: the unsigned int argument is converted to binary
  • Print_Binary

task3

Handle the following conversion specifiers:

• u:

  • Print_Unsigned

• o:

  • Print_Octal

• x:

  • Print_Hexadecimal
  • Print_Lower_Hex_Chars

• X:

  • Print_Hexadecimal
  • Print_Upper_Hex_Chars

• You don’t have to handle the flag characters

• You don’t have to handle field width

• You don’t have to handle precision

• You don’t have to handle the length modifiers

task4

Use a local buffer of 1024 chars in order to call write as little as possible.

• buffer

task5

Handle the following custom conversion specifier:

• S : prints the string. Print_String
• Non printable characters (0 < ASCII value < 32 or >= 127) are printed this way: \x, followed by the ASCII code value in hexadecimal (upper case - always 2 characters)
  • Print_Non-Printable_Chars

task6

Handle the following conversion specifier: p.

• You don’t have to handle the flag characters
• You don’t have to handle field width
• You don’t have to handle precision
• You don’t have to handle the length modifiers
  • Print_Pointer

task7

Handle the following flag characters for non-custom conversion specifiers:

• +
• space
• #

task8

Handle the following length modifiers for non-custom conversion specifiers:

• l

• h

• Conversion specifiers to handle: d, i, u, o, x, X

task9

Handle the field width for non-custom conversion specifiers.

• Handle_Field_Width

task10

Handle the precision for non-custom conversion specifiers.

• Handle_Precision

task11

Handle the 0 flag character for non-custom conversion specifiers.

• Handle_0_Flag

task12

Handle the - flag character for non-custom conversion specifiers.

• Handle_-_Flag

task13

Handle the following custom conversion specifier:

• r : prints the reversed string.
  • Handle_String_Reverse

task14

Handle the following custom conversion specifier:

• R: prints the rot13'ed string
  • Rot13_Encryption

task15

All the above options work well together.

• header_file

Pseudocode

draw.io Pseudocode_For_Printf

Flow-Chart Diagram

Implementation

1. The function takes a format string and a variable number of arguments.

2. It initialises variables including an integer i, printed, printed_chars, flags, width, precision, size, buff_ind, a char buffer with a size of BUFF_SIZE and a va_list named list

3. The function checks if the format string is NULL and returns -1 if it is.

4. It initialises the variable argument list and sets the buffer index to 0 and the printed characters to 0.

5. The function iterates through the format string, for each iteration it checks if the current character is not '%'

6. If the current character is not '%', it adds the character to the buffer and increments the buffer index by 1.

7. If the buffer index reaches the size of the buffer, it calls the print_buffer function to print the buffer.

8. If the current character is "%", it calls the helper functions get_flags, get_width, get_precision, get_size and handle_print to process the formatting

9. It prints the output to the buffer and increments the printed_chars by the number of characters printed.

10. At the end of the iteration; it calls the print_buffer function to print whatever is left in the buffer.

11. The function ends the variable argument list and returns the total number of characters printed.

Collaborators

• Yasmine Ben Ali
• Samuel Selasi