ft_printf

42 C: printf

A simple printf clone written in Norm-compliant C.

⚠️ Please don't actually use this in production

Building

To build our project, make sure to recursively clone the submodules by passing --recurse. Other than that, simple run make in the project's root. This will make the libftprintf.a library file.

Modularity

This printf writes through a writer struct in order to allow for creation of modular printf derivatives. This allows us to write not only to the output, but also to: files, strings, sockets, mail pidgeons, etc! A writer looks like this:

struct {
    / How many bytes we wrote
    |                      / A reference to the state pointer
    |                      |                   / The string  / The string length
    v                      v                   v             v
  ssize_t  (*write)(struct s_writer *self, char *str, size_t length);

  // Internal state to be passed to the write call.
  void  *state;
};

Functions

I/O

// Writes to standard output (is call to fprintf)
int ft_printf(char *fmt, ...);

// Writes to a file descriptor.
int ft_dprintf(int fd, char *fmt, ...);

Strings

// Writes to a *new* string see example 1.
int ft_asprintf(char **dest, char *fmt, ...);

// Writes to a string (does not check size, dangerous!)
int ft_sprintf(char *dest, char *fmt, ...);

// Writes to a string, taking a limit.
int ft_snprintf(char *dest, size_t len, char *fmt, ...);

Examples

Example 1.

char *str;

str = NULL;
ft_aprintf(&str, "Hello, %s", "world!");
// `str' will now have `Hello, world!'

Tests

Testing framework

Our printf uses criterion for tests. All of our tests are ran on the snprintf writer and the asprintf writer only. As well as some internal tests.

Running them

To run the tests, go into test/, and run the following command: make test. This will run the tests.

Debugging

Snippet to print the current output string when in lldb and you are in a ft_asprintf formatter:

p *((struct s_writer_alloc_state *)((t_writer *)writer)->state)->str_ptr