feat(stdio): scanf family

include/stdio.h

@@ -429,4 +429,35 @@ fmemopen(void *buf, size_t size, const char *mode);
 FILE *
 open_memstream(char **ptr, size_t *sizeloc);
 
+/* formatted input (todo 17) */
+
+/*
+ * Read formatted input. scanf reads from stdin, fscanf from the stream,
+ * sscanf from the string. The conversion directives are %d %i %u %o %x %X
+ * %f %F %e %E %g %G %a %A %c %s %[ %p %n and %% (with assignment
+ * suppression '*', a decimal field width, and the length modifiers hh h l
+ * ll j z t, plus L for the float conversions). A conversion fails to match
+ * without consuming its offending character; the return value is the
+ * number of assigned (non-suppressed) input items, or EOF if an input
+ * failure occurs before the first one. Integer overflow stores a saturated
+ * value and sets errno = ERANGE (nothing else touches errno).
+ */
+int
+scanf(const char *restrict format, ...);
+
+int
+fscanf(FILE *restrict stream, const char *restrict format, ...);
+
+int
+sscanf(const char *restrict s, const char *restrict format, ...);
+
+int
+vscanf(const char *restrict format, va_list ap);
+
+int
+vfscanf(FILE *restrict stream, const char *restrict format, va_list ap);
+
+int
+vsscanf(const char *restrict s, const char *restrict format, va_list ap);
+
 #endif /* VLIBC_STDIO_H */