create a C string from a format without manually allocating a buffer

sprintfalloc

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>

int strappend (char ** buff, int alloclen, const char * nstring) {
	int slen = strlen(buff[0]);
	int slen2 = strlen(nstring);
	char * newbuff = (char *)malloc(slen + slen2 + 2);
	memset(newbuff, 0, slen+slen2+2);
	memcpy(newbuff, buff[0], slen);
	memcpy(&newbuff[slen], nstring, slen2);
	free(buff[0]);
	buff[0] = newbuff;
	return (slen + slen2 + 2);
}

char * makestring (char * fmt, ...) {
	va_list listPointer;
	int count = 0, len = strlen(fmt);
	int i;
	for (i = 0; i < len; i++) {
		if (fmt[i] == '%') {
			if (i + 1 < len) {
				if (fmt[i+1] != '%') {
					count += 1;
				}
			}
		}
	}
	va_start (listPointer, fmt);
	// now we can calculate total length
	char * mstr = (char *)malloc(1);
	mstr[0] = 0;
	int alloclen = 1;
	for (i = 0; i < len; i++) {
		char c = fmt[i];
		if (i + 1 < len && c == '%') {
			char nc = fmt[++i];
			if (nc == 's') {
				// append string
				const char * ms = va_arg (listPointer, const char*);
				alloclen = strappend(&mstr, alloclen, ms);
			} else if (nc == 'd') {
				int ic = va_arg (listPointer, int);
				char ms[20];
				sprintf(ms, "%d", ic);
				alloclen = strappend(&mstr, alloclen, ms);
			} else if (nc == 'p') {
				void * ic = va_arg (listPointer, void*);
				char ms[20];
				sprintf(ms, "%p", ic);
				alloclen = strappend(&mstr, alloclen, ms);
			} else if (nc == 'f') {
				double ic = va_arg (listPointer, double);
				char ms[20];
				sprintf(ms, "%lf", ic);
				alloclen = strappend(&mstr, alloclen, ms);
			} else if (nc == '%') {
				alloclen = strappend(&mstr, alloclen, "%");
			}
		} else {
			char str[2];
			sprintf(str, "%c", c);
			alloclen = strappend(&mstr, alloclen, str);
		}
	}
	va_end (listPointer);
	return mstr;
}

int main (int argc, char * argv[]) {
	char * str = makestring("hello %s!\n%d%% complete\n", "world!", 100);
	printf("%s", str);
	free(str);
	str = makestring("pi = %f\n", 3.141592);
	printf("%s", str);
	free(str);
	return 0;
}