ft_printf

A minimal, 42-school–style reimplementation of the C standard printf function.

This project provides:

• A ft_printf function that writes formatted output to standard output using only low-level syscalls (write).
• A static library libftprintf.a that you can link against in your C projects.

Supported conversions:

• Characters: %c
• Strings: %s
• Pointers: %p (printed as 0x...)
• Signed decimal: %d, %i
• Unsigned decimal: %u
• Hexadecimal (lowercase): %x
• Hexadecimal (uppercase): %X
• Percent sign: %%

Limitations:

• Width, precision, flags, and length modifiers are not implemented.
• Output goes to stdout (file descriptor 1).
• The function returns the number of characters written, or -1 on error.

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Build

The project ships with a simple Makefile.

Targets:

• make or make all — builds libftprintf.a
• make clean — removes object files
• make fclean — removes object files and the library
• make re — full rebuild

Resulting artifact:

• libftprintf.a

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Usage

1. Build the library:

make

2. Include the header in your source:

#include "ft_printf.h"

3. Compile and link:

cc -Wall -Wextra -Werror your_main.c libftprintf.a -o your_program
# or using -L/-l:
cc -Wall -Wextra -Werror your_main.c -L. -lftprintf -o your_program

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API

int ft_printf(const char *s, ...);

Behavior:

• Parses the format string s and consumes variadic arguments.
• Writes to standard output.
• Returns the total number of characters written, or -1 if a write error occurs.

Note:

• Internal helper functions are declared in ft_printf.h for compilation but are not intended to be used directly by external code.

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Examples

Basic usage:

#include "ft_printf.h"

int main(void)
{
    int n = 42;
    char *str = "hello";
    void *ptr = str;

    ft_printf("Char: %c\n", 'A');
    ft_printf("String: %s\n", str);
    ft_printf("Signed: %d, %i\n", n, -n);
    ft_printf("Unsigned: %u\n", 3000000000u);
    ft_printf("Hex low: %x\n", 48879);     // beef
    ft_printf("Hex up : %X\n", 48879);     // BEEF
    ft_printf("Pointer: %p\n", ptr);
    ft_printf("Percent: %%\n");

    return 0;
}

Expected output (example):

Char: A
String: hello
Signed: 42, -42
Unsigned: 3000000000
Hex low: beef
Hex up : BEEF
Pointer: 0x...
Percent: %

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Repository structure

• Makefile — builds the static library
• ft_printf.h — public header (API)
• ft_printf.c — main formatter and dispatcher
• ft_putc.c — character output
• ft_putstr.c — string output
• ft_int.c — signed integer output (decimal)
• ft_llu.c — unsigned integer output (decimal)
• ft_putlew.c — lowercase hexadecimal output
• ft_putup.c — uppercase hexadecimal output
• ft_voidx0.c — pointer output (0x prefix + hex)

Library name:

• libftprintf.a

Compiler flags (from Makefile):

• -Wall -Wextra -Werror

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Testing quickly

Create a small test file:

// main.c
#include "ft_printf.h"

int main(void)
{
    int ret = ft_printf("Hello %s (%d) 0x%x %%\n", "world", 42, 0xBEEF);
    ft_printf("Printed %d chars\n", ret);
    return 0;
}

Build and run:

cc -Wall -Wextra -Werror main.c libftprintf.a -o test && ./test

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Notes

• The project focuses on correctness for the supported conversions and simplicity of implementation.
• Error handling: the function checks write availability early and returns -1 on error.

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Author

• @otmansabir