Parse a printf-like format string

wparsef.c

#include <wchar.h>

typedef struct {
        wchar_t cs;
        wchar_t flags[8];
        wchar_t mod[3];
        int w;
        int len;
} Printf;

int
wparsef(Printf *pf, wchar_t *fmt) {
	wchar_t *p = fmt, num[32];
	int i;

	if(*p != '%' || *++p == '%')
		return -1;
	pf->w = pf->len = 0;
	/* flags */
	i = 0;
	while(*p == '#' || *p == '0' || *p == '-' || *p == ' '
	|| *p == '+' || *p == '\'' || *p == 'I') {
		pf->flags[i++] = *p;
		++p;
	}
	pf->flags[i] = '\0';
	/* padding */
	if(*p == '*') {
		pf->w = -1;
		++p;
	}
	else if(*p >= '0' && *p <= '9') {
		i = 0;
		while(*p >= '0' && *p <= '9')
			num[i++] = *p++;
		num[i] = '\0';
		pf->w = wcstol(num, NULL, 10);
	}
	/* truncation */
	if(*p == '.' && *++p) {
		if(*p == '*') {
			pf->len = -1;
			++p;
		}
		else if(*p >= '0' && *p <= '9') {
			i = 0;
			while(*p >= '0' && *p <= '9')
				num[i++] = *p++;
			num[i] = '\0';
			pf->len = wcstol(num, NULL, 10);
		}
	}
	/* modifier */
	i = 0;
	if(*p == 'h' || *p == 'l' || *p == 'q' || *p == 'L'
	|| *p == 'j' || *p == 'z' || *p == 'Z' || *p == 't') {
		pf->mod[i++] = *p++;
		if((*p == 'l' || *p == 'h') && *(p+1) == *p)
			pf->mod[i++] = *p++;
	}
	pf->mod[i] = '\0';
	pf->cs = *p;
	return p - fmt;
}