I need help with ft_printf bonus

[u/Mysterious-Frame2218]

Hey guys, I just finished the mandatory part of ft_printf and I'm ready to tackle the bonuses, but I'm not sure where to start. Do you have any tips or strategies on how to implement them? What tools or approaches worked best for you?

[u/Axman6]

What are you talking about? The number of people on the internet with no theory of mind is astounding. 

[u/Mysterious-Frame2218 → u/Axman6]

sorry, I should have give more context.
I'm working on an implementation of the printf function and I need insights on how to handle certain flags like .#0-+space.

[u/WittyStick → u/Mysterious-Frame2218]

You basically want a boolean flag for each modifier.

bool alt_flag = false;          // '#'
bool left_flag = false;         // '-'
bool sign_flag = false;         // '+'
bool space_flag = false;        // ' '
char padding_char = ' ';        // default space but may be overridden to '0'

Simplest way to parse is a switch on the character with continue where it finds one of them and break if not. fmt is a const char *.

bool doneflags = false;
while (!doneflags && *fmt) 
{
    switch (*fmt++)
    {
        case '#':
            spec->alt_flag = true;
            continue;
        case '-':
            spec->left_flag = true;
            continue;
        case '+':
            spec->sign_flag = true;
            continue;
        case ' ':
            spec->space_flag = true;
            continue;
        case '0':
            spec->padding_char = '0';
            continue;
        default:
            doneflags = true;
            fmt--;
            break;
    }
}

If you want to be pedantic you could test if each flag is already set and handle the case where they appear more than once.

If both ' ' and '-' are parsed, the space is ignored.

if (left_flag)
    space_flag = false;

Next, width is either provided as an extra arg or is a number

bool extra_width_arg = false;  // '*'
int width = 0;

if (*fmt == '*') 
{
    fmt++;
    extra_width_arg = true;
}
else 
{
    while (*fmt >= '0' && *fmt <= '9')
        width = width * 10 + (*fmt++ - '0');
}

Precision is similar, but with a prior check for '.'.

bool extra_prec_arg = false;   // '.*'
int prec = 0;

if (*fmt == '.')
{
    fmt++;
    if (*fmt == '*') 
    {
        fmt++;
        extra_prec_arg = true;
    }
    else 
    {
        while (*fmt >= '0' && *fmt <= '9')
            prec = prec * 10 + (*fmt++ - '0');
    }
}

In both of the above cases you need to check width or prec doesn't overflow. The standard requires them to fit into an int.

Then there should only be one length modifier present, so we can use an enum instead of a boolean flag per modifier.

enum {
    lm_none,
    lm_byte,        // "hh"
    lm_short,       // "h"
    lm_long,        // "l"
    lm_long_long,   // "ll"
    lm_long_dbl,    // "L"
    lm_size,        // "z"
    lm_ptrdiff,     // "t"
    lm_intmax,      // "j"
} length_modifier = lm_none;

switch (*fmt++)
{
    case 'h':
        if (*fmt == 'h') 
        {
            fmt++;
            length_modifier = lm_byte;
        }
        else
            length_modifier = lm_short;
        break;
    case 'j':
        length_modifier = lm_intmax;
        break;
    case 'L':
        length_modifier = lm_long_dbl;
        break;
    case 'l':
        if (*fmt == 'l') 
        {
            fmt++;
            length_modifier = lm_long_long;
        }
        else
            length_modifier = lm_long;
        break;
    case 't':
        length_modifier = lm_ptrdiff;
        break;
    case 'z':
        length_modifier = lm_size;
        break;
    default:
        fmt--;
        break;
}

Last you would parse the conversion specifier with another switch. In each case you can test which flags/modifiers have already been set.

[u/Electronic_Fan5938 → u/Axman6]

Saying this is probably the most "lacking theory of mind" thing you could possibly do.

Someone omits context so you decide to be accuse the other person of lacking theory of mind? 😂 Yea man, be the change you wanna see in the world.

[u/Axman6 → u/Electronic_Fan5938]

Not understanding what context others might have is precisely what a lack of theory of mind is.

My car is broken, can you fix it? I know what’s wrong, so you must know that too!

Asking good questions is a very important life skill that seems to be completely dying. 

[u/Electronic_Fan5938 → u/Axman6]

Not understanding how to deal with someone who has omitted context without accusing them of lacking theory of mind is exactly what lacking theory of mind is. 😂😂

[u/burei00x_]

You need to add some context, not everyone knows what this assignment is. I'm a 42 student and I'd advise you to look into the IEEE754 floating point standard. Not sure of all the formats you have to handle for the bonuses but I'm almost certain the floating point formatter is the hardest one to implement. I think some old slack post about this bonus still exists somewhere on the intranet. Best of luck in your endeavors

[u/zedin27 → u/burei00x_]

This is a good starting point. I would also suggest hash tables and bitmasking

[u/ef3d0c3e → u/burei00x_]

Floats are not part of the bonuses, thankfully.
I got curios when I did this project and it turns out that formatting floats accurately is extremely tedious.

I found this https://ranjitjhala.github.io/static/fp-printing-popl16.pdf which is an accessible read about formatting (and parsing) floats. One caveat is that you always need high precision when formatting. For floats you can use doubles, but for doubles you have to implement your own higher precision floating point numbers.

I found this implementation which is short and easier to understand than the libc implementation you could have on your machine: https://github.com/tobybell/print-float

[u/burei00x_ → u/ef3d0c3e]

Weird, floats were part of the bonus when I did this project about 8 months ago. I didn't do it for the exact reasons you said because I wanted to advance in the curriculum, but still, it's a very good exercise to wrap your head around how fp are represented.

[u/Mysterious-Frame2218 → u/burei00x_]

thank you, I'll check it out!

[u/zedin27]

Mmm fellow 42 student