Split arraddn into pointer and index return

stb_ds.h

@@ -108,11 +108,16 @@ DOCUMENTATION
           Inserts n uninitialized items into array a starting at a[p],
           moving the rest of the array over.
 
-      arraddn:
-        T* arraddn(T* a, int n)
+      arraddnptr:
+        T* arraddnptr(T* a, int n)
           Appends n uninitialized items onto array at the end.
           Returns a pointer to the first uninitialized item added.
 
+      arraddnoff:
+        size_t arraddnoff(T* a, int n)
+          Appends n uninitialized items onto array at the end.
+          Returns the index of the first uninitialized item added.
+
       arrdel:
         void arrdel(T* a, int p);
           Deletes the element at a[p], moving the rest of the array over.
@@ -390,7 +395,8 @@ CREDITS
 #define arrpush     stbds_arrput
 #define arrpop      stbds_arrpop
 #define arrfree     stbds_arrfree
-#define arraddn     stbds_arraddn
+#define arraddnptr  stbds_arraddnptr
+#define arraddnoff  stbds_arraddnoff
 #define arrsetlen   stbds_arrsetlen
 #define arrlast     stbds_arrlast
 #define arrins      stbds_arrins
@@ -522,7 +528,8 @@ extern void * stbds_shmode_func(size_t elemsize, int mode);
 #define stbds_arrput(a,v)     (stbds_arrmaybegrow(a,1), (a)[stbds_header(a)->length++] = (v))
 #define stbds_arrpush         stbds_arrput  // synonym
 #define stbds_arrpop(a)       (stbds_header(a)->length--, (a)[stbds_header(a)->length])
-#define stbds_arraddn(a,n)    (stbds_arrmaybegrow(a,n), stbds_header(a)->length += (n), &(a)[stbds_header(a)->length-(n)])
+#define stbds_arraddnptr(a,n) (stbds_arrmaybegrow(a,n), stbds_header(a)->length += (n), &(a)[stbds_header(a)->length-(n)])
+#define stbds_arraddnoff(a,n) (stbds_arrmaybegrow(a,n), stbds_header(a)->length += (n), stbds_header(a)->length-(n))
 #define stbds_arrlast(a)      ((a)[stbds_header(a)->length-1])
 #define stbds_arrfree(a)      ((void) ((a) ? STBDS_FREE(NULL,stbds_header(a)) : (void)0), (a)=NULL)
 #define stbds_arrdel(a,i)     stbds_arrdeln(a,i,1)