MY_PRINTF

To see how it works:

git clone https://github.com/kasavine/my_printf.git
cd my_printf

Compile: gcc my_printf.c test.c
Run: ./a.out

• int my_printf(char * restrict format, ...);
• my_printf() function writes output to stdout - the standard output stream.

After the %, the following appear in sequence:

• doux The int argument is converted to:
  • signed decimal (d)
  • unsigned octal (o)
  • unsigned decimal (u)
  • unsigned hexadecimal (x).
• c The int argument is converted to an unsigned char, and the resulting character is written.
• s The char * argument is expected to be a pointer to an array of character type (pointer to a string). Characters from the array are written up to (but not including) a terminating NUL character.
• p The void * pointer argument is printed in hexadecimal.

What I have learnt?

• variadic functions (can receive an unknown amount of arguments and you can cycle through them using a specific library)
• variable argument lists

Declararion of the variadic function - do it like you usually do and add three dots "..." as the last argument. It means that there is possibility of additional arguments, but it is not mandatory.

The printf is probably the most notable function that uses this principle. The printf will take N amount of arguments and has many different parameters to format the output it will print.

<stdarg.h>

• macro va_list: to initialize the arguments pointer
• macro va_start: to point to the first element (of the mandatory one(s)
• macro va_arg: to point to the first of the optional arguments the user entered and every time it is called it will move over to the next argument
• macro va_end: GCC will not even notice it but you could still add it in case you use a different compiler
• macro va_copy:

The list is declared by using the va_list macro, then the user checks if the list is empty or not.

• print a character
• print a set of characters - string (char *)
• print signed decimal
• print unsigned decimal
• print unsigned octal
• print unsigned hexadecimal
• print the address of pointer - hexadecimal with 0x....
• -g3 -fsanitize=address (test code against memory errors by compiling with the debugging flags)
• -Wall -Wextra -Werror (code must be compiled with the flags)
• Allowed to use: write, malloc, free, stdarg.h