Refactoring: Add a utility function

chibicc.h

@@ -10,6 +10,12 @@
 typedef struct Type Type;
 typedef struct Node Node;
 
+//
+// strings.c
+//
+
+char *format(char *fmt, ...);
+
 //
 // tokenize.c
 //

parse.c

@@ -108,9 +108,7 @@ static Obj *new_gvar(char *name, Type *ty) {
 
 static char *new_unique_name(void) {
   static int id = 0;
-  char *buf = calloc(1, 20);
-  sprintf(buf, ".L..%d", id++);
-  return buf;
+  return format(".L..%d", id++);
 }
 
 static Obj *new_anon_gvar(Type *ty) {

strings.c

@@ -0,0 +1,15 @@
+#include "chibicc.h"
+
+// Takes a printf-style format string and returns a formatted string.
+char *format(char *fmt, ...) {
+  char *buf;
+  size_t buflen;
+  FILE *out = open_memstream(&buf, &buflen);
+
+  va_list ap;
+  va_start(ap, fmt);
+  vfprintf(out, fmt, ap);
+  va_end(ap);
+  fclose(out);
+  return buf;
+}