my_printf | ETNA project made in 5 days | Graphics library

You can't use preprocessor directives while defining a #define. This means that your #ifdef USE_WRITE_DEBUG_INFO won't work.

For this case, use a function rather than a macro:

In your main function, you're calling free on list_b, but it is uninitialized meaning its valid is indeterminate. Attempting to call free on such a pointer invokes undefined behavior which causes a crash.

Get rid of that call to free, and in fact remove list_b entirely as it isn't being used.

Also, calling free at the end of display_list doesn't make sense because you don't need to clean up any memory here. You get away with it because the value of tmp is NULL at this point, and calling free on a NULL pointer is a no-op.

You also have list_a uninitialized. This results in your list having an invalid pointer at the end. You should initialize it to NULL.

With #include "my_printf.h" the preprocessor will look for a file named my_printf.h in the folder in which you are compiling, you need to add the full path to it to include properly:

Because there's variant of printf that expects a va_list argument. If you have a va_list you must use the functions with the v prefix, such as vprintf.

The call to printf leads to undefined behavior.

I believe you’re looking for snprintf which is similar to printf except that the output is stored in an array rather than printed. snprintf would be used like so: