stdio - Standard I/O

Header: libc/include/stdio.h
Sources: libc/stdio/printf.c, libc/stdio/putchar.c, libc/stdio/puts.c

Provides the minimal subset of <stdio.h> needed by the kernel.

Constants

#define EOF (-1)

Returned by character-output functions on failure.

Functions

putchar

int putchar(int c);

Write the character (char)c to the terminal. The concrete implementation is provided by the kernel’s tty.c via the linker (not in libc itself), which calls t_putchar. Returns c on success, EOF on failure.

This is the single output primitive on which printf and puts are built.

puts

int puts(const char *s);

Write the null-terminated string s to the terminal followed by a newline ('\n'). Returns a non-negative value on success, EOF on failure.

printf

int printf(const char *restrict format, ...);

Write a formatted string to the terminal. Returns the number of characters written, or -1 on error.

Supported format specifiers:

Unsupported specifiers (e.g. %d, %x, %u) are passed through verbatim as a fallback - the format string from the first unrecognised % is printed unchanged.

Future work

• Add %d / %i (signed decimal), %u (unsigned decimal), %x / %X (hexadecimal), and %p (pointer) specifiers to printf.
• Add snprintf / vsnprintf for safe formatted output into buffers, needed by subsystems that build strings before writing them to the terminal or serial port.