This project has been created as part of the 42 curriculum by caide-so.

ft_printf

Description

This project consists of reimplementing the printf() function from the C standard library.

This README focuses exclusively on the bonus part, which extends the mandatory implementation by handling:

• Field minimum width
• Flags: -, 0, ., #, (space), +
• Any valid combination of these flags
• All mandatory conversions (cspdiuxX%) with full flag interaction

The bonus part is evaluated only if the mandatory part is perfect.

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Features Implemented

Supported Flags

Flag	Behavior
-	Left-align within the given field width
0	Zero-padding (ignored if - is present or precision is set)
.	Precision handling (numbers and strings)
#	Alternate form (0x, 0X, 0)
	Space prefix for positive numbers
+	Explicit sign for positive numbers

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Field Minimum Width

• Pads output to match a specified minimum width.
• Padding can be spaces or zeroes depending on flags.
• Correct interaction with precision and alignment.

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Parsing Strategy

The bonus implementation relies on a format state structure storing:

• Flags
• Width
• Precision
• Conversion type

Conceptual structure:

typedef struct s_format
{
    int minus;
    int zero;
    int dot;
    int hash;
    int space;
    int plus;
    int width;
    int precision;
    char type;
}   t_format;

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Algorithm Explanation

Format Parsing

When encountering %, the parser:

1. Initializes a format structure.
2. Parses flags.
3. Parses width.
4. Parses precision.
5. Stores conversion type.
6. Dispatches to the correct handler.

Formatting Order (Numbers)

1. Determine sign or prefix.
2. Apply precision.
3. Compute final length.
4. Apply width padding.
5. Apply alignment if needed.

Flag Interaction Rules

• - overrides 0
• Precision disables 0 for numeric conversions
• + overrides space
• # applies only for non-zero hexadecimal values
• Precision 0 with value 0 prints nothing (except width padding)

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Data Structure Justification

The structured parsing approach:

• Separates parsing from printing
• Prevents duplicated logic
• Keeps the implementation extensible
• Avoids complex nested conditionals

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Compilation

make bonus

Rules:

make
make bonus
make clean
make fclean
make re

Compiled with:

-Wall -Wextra -Werror

Library generated:

libftprintf.a

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Testing Philosophy

Tested against the original printf() with:

• Complex flag combinations
• Width and precision edge cases
• Zero and NULL behavior
• Alignment interactions

Goal: strict behavior equivalence.

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Resources

• https://man7.org/linux/man-pages/man3/printf.3.html
• https://en.cppreference.com/w/c/io/fprintf
• ISO C99 Standard — Formatted Output
• Variadic Functions — stdarg.h documentation

AI Usage Disclosure

AI was used only for documentation clarification and validation of edge-case behavior.

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Author

caide-so — caide-so@student.42sp.org.br