ft_printf

What is printf?

printf is a function in the C standard library that allows you to print formatted output to the console. It is a variadic function, which means it can take a variable number of arguments. The first argument is a format string that specifies how to format the output, and the remaining arguments are the values to be printed.

Make sure to read the intro and understand how Variadic Functions work. This will help you understand how to implement your own version of printf.

Implementation

// ft_printf.c
#include "ft_printf.h"
 
int	ft_printf(const char *str, ...)
{
	va_list	args;
	int		len;
 
	va_start(args, str);
	len = 0;
	while (*str)
	{
		if (*str == '%')
		{
			str++;
			if (*str == '\0')
				break ;
			ft_handle_specifiers(*str, &len, args); // handle c, s, p, d, i, u, x, X, %
		}
		else
			len += write(1, str, 1);
		str++;
	}
	va_end(args);
	return (len);
}

// ft_printf.h
 
#ifndef FT_PRINTF_H
#define FT_PRINTF_H
 
#include <stdarg.h>
#include <stdlib.h>
#include <unistd.h>
 
int ft_printf(const char *str, ...);
void ft_handle_specifiers(char current_char, int *len, va_list args);
int ft_putstr(char *s);
int ft_putnbr(int n);
int ft_putnbr_base(unsigned long value, int specifier);
char *ft_strchr(const char *str, int c);
 
#endif

// handlers.c
 
#include "ft_printf.h"
 
static void	ft_handle_char(int *len, va_list args);
static void	ft_handle_string(int *len, va_list args);
static void	ft_handle_pointer(int *len, va_list args);
static void	ft_handle_number(char specifier, int *len, va_list args);
 
void	ft_handle_specifiers(char current_char, int *len, va_list args)
{
	if (current_char == 'c')
		ft_handle_char(len, args);
	else if (current_char == 's')
		ft_handle_string(len, args);
	else if (current_char == 'p')
		ft_handle_pointer(len, args);
	else if (ft_strchr("uxXdi", current_char))
		ft_handle_number(current_char, len, args);
	else if (current_char == '%')
		*len += write(1, "%", 1);
}
 
static void	ft_handle_char(int *len, va_list args)
{
    char c;
	c = va_arg(args, int);
	*len += write(1, &c, 1);
}
 
static void	ft_handle_string(int *len, va_list args)
{
    char *temp_s;
	temp_s = va_arg(args, char *);
	if (temp_s == NULL)
		*len += write(1, "(null)", 6);
	else
		*len += ft_putstr(temp_s);
}
 
static void	ft_handle_pointer(int *len, va_list args)
{
	unsigned long ptr;
 
	ptr = va_arg(args, unsigned long);
	if (!ptr)
		*len += ft_putstr("(nil)");
	else
		*len += ft_putstr("0x") + ft_putnbr_base(ptr, 'p');
}
 
static void	ft_handle_number(char specifier, int *len, va_list args)
{
	if (specifier == 'd' || specifier == 'i')
		*len += ft_putnbr(va_arg(args, int));
	else if (ft_strchr("uxX", specifier))
		*len += ft_putnbr_base(va_arg(args, unsigned int), specifier);
}

// helpers.c
 
#include "ft_printf.h"
 
int	ft_putstr(char *s)
{
	int	i;
 
	i = 0;
	while (s[i])
		write(1, &s[i++], 1);
	return (i);
}
 
int	ft_putnbr_base(unsigned long value, int specifier)
{
	char	*base;
	int		base_len;
	int		len;
 
	if (specifier == 'u')
		base = "0123456789";
	else if (specifier == 'x' || specifier == 'p')
		base = "0123456789abcdef";
	else if (specifier == 'X')
		base = "0123456789ABCDEF";
	base_len = 0;
	len = 0;
	while (base[base_len])
		base_len++;
	if (value >= (unsigned long)base_len)
		len += ft_putnbr_base(value / base_len, specifier);
	write(1, &base[value % base_len], 1);
	return (len + 1);
}
 
int	ft_putnbr(int n)
{
	char	num;
	int		len;
 
	len = 0;
	if (n == -2147483648)
	{
		len += write(1, "-2147483648", 11);
	}
	else if (n < 0)
	{
		len += write(1, "-", 1);
		len += ft_putnbr(n * (-1));
	}
	else if (n > 9)
	{
		len += ft_putnbr(n / 10);
		len += ft_putnbr(n % 10);
	}
	else
	{
		num = n + '0';
		len += write(1, &num, 1);
	}
	return (len);
}
 
char	*ft_strchr(const char *str, int c)
{
	while (*str != '\0')
	{
		if (*str == (char)c)
		{
			return ((char *)str);
		}
		str++;
	}
	if (c == '\0')
	{
		return ((char *)str);
	}
	return (NULL);
}