diff --git a/README.md b/README.md
index f98d21b..6e905b7 100644
--- a/README.md
+++ b/README.md
@@ -79,7 +79,7 @@ segarray *-- ringbuf : 组合
 segarray *-- rawbuf : 组合
 
 arraylist *-- darray : 组合
-string *-- darray : 组合
+string *-- arraylist : 组合
 hashtable *-- darray : 组合
 
 
@@ -107,22 +107,26 @@ equeue ..> ringbuf : 依赖
 ## 数据结构
 
 ### 底层基础容器
-> 原生裸数据结构
 
 |数据结构 |名称 |说明 |
 |---|---|---|
-| darray  | 动态数组 | 扩容
-| ringbuf   | 环形缓存区 | 扩容/外部缓存 
 | linklist   | 单链表 | 
 | dlinklist   | 双向链表 |
+| darray  | 动态数组 | 扩容
+| ringbuf   | 环形缓存区 | 扩容/外部缓存 
 | rawbuf | 原始缓冲区 | 动态分配固定容量/外部缓存
 | segarray | 分段数组 | 扩容
 
+### 中层容器
+|数据结构 |名称 |说明 |
+|---|---|---|
+| segarray | 分段数组 | 扩容
+| arraylist | 动态数组 | 扩容（负索引/切片）
+
 **使用建议**
 - ringbuf 小数据，少库容
 - segarray 大数据，优先扩容
 
-
 ### 通用标准容器
 > 基于底层封装
 
@@ -131,6 +135,7 @@ equeue ..> ringbuf : 依赖
 | deque  | 双端队列 | 扩容
 | stack  | 栈 | 扩容
 | queue  | 队列 | 扩容
+| ustring | 字符串 | 扩容
 
 ### 嵌入式专用容器
 > 适配嵌入式场景、外置内存、无动态堆分配
@@ -192,6 +197,7 @@ size_t index(void *obj);                // 获取元素索引, -1为不存在
 
 bool insert(size_t index, const void* obj);     // 插入元素
 bool remove(size_t index, const void *obj);     // 删除元素 < delete !!!废弃：防止项目用于C++，关键字冲突>
+bool erase(size_t index, size_t count);         // 删除区间元素
 
 // 随机访问
 bool set(uint32_t index, const void* obj);      // 设置元素
diff --git a/src/darray.c b/src/darray.c
index 72f3808..227b829 100644
--- a/src/darray.c
+++ b/src/darray.c
@@ -238,7 +238,7 @@ bool darray_iter_hasnext(struct _iterator *iter)
     }
     else
     {
-        if (iter->_index == 0)
+        if (iter->_index == -1)
         {
             return false;
         }
diff --git a/src/ringbuf.c b/src/ringbuf.c
index 740d694..d4c979a 100644
--- a/src/ringbuf.c
+++ b/src/ringbuf.c
@@ -306,7 +306,7 @@ bool ringbuf_iter_hasnext(struct _iterator *iter)
     }
     else
     {
-        if (iter->_index == self->_head)
+        if (iter->_index == ring_index_prev(self->_head, self->_capacity))
         {
             return false;
         }
diff --git a/src/segarray.c b/src/segarray.c
index de9aa13..ae020a1 100644
--- a/src/segarray.c
+++ b/src/segarray.c
@@ -636,7 +636,7 @@ bool segarray_iter_hasnext(struct _iterator *iter)
     }
     else
     {
-        if (iter->_index == 0)
+        if (iter->_index == -1)
         {
             return false;
         }
diff --git a/src/ustring.c b/src/ustring.c
index 0ec43d2..e88fdf4 100644
--- a/src/ustring.c
+++ b/src/ustring.c
@@ -324,7 +324,7 @@ bool ustring_iter_hasnext(struct _iterator *iter)
     }
     else
     {
-        if (iter->_index == 0)
+        if (iter->_index == (size_t)-1)
         {
             return false;
         }
@@ -348,7 +348,7 @@ const void *ustring_iter_next(struct _iterator *iter)
     {
         iter->_index = iter->_index - 1;
     }
-    return self->_alist->at(self->_alist, index);
+    return self->at(self, index);
 }
 
 iterator_t ustring_iter(struct _ustring *self, linear_order_t order)
@@ -367,7 +367,6 @@ iterator_t ustring_iter(struct _ustring *self, linear_order_t order)
     {
         iter->_index = self->len(self) - 1;
     }
-
     iter->hasnext = ustring_iter_hasnext;
     iter->next = ustring_iter_next;
     return iter;
@@ -394,8 +393,8 @@ static size_t ustring_count(struct _ustring *self, uview_t uvstr)
 {
     unicstl_assert(self != NULL);
     size_t count = 0;
-    char *p = self->cstr(self);
-    while(p != '\0')
+    char *p = (char *)self->cstr(self);
+    while(*p != '\0')
     {
         p = strstr(p, uvstr.str);
         if(p == NULL)
diff --git a/test/test.h b/test/test.h
index a7236d2..b251af5 100644
--- a/test/test.h
+++ b/test/test.h
@@ -20,7 +20,7 @@
 #include "unity.h"
 
 
-#define UNITTEST_ALL        0
+#define UNITTEST_ALL        1
 
 #define UNITTEST_LINKLIST   (UNITTEST_ALL || 0)
 #define UNITTEST_DLINKLIST  (UNITTEST_ALL || 0)
diff --git a/test/test_arraylist.c b/test/test_arraylist.c
index f7d3ac2..4d110c9 100644
--- a/test/test_arraylist.c
+++ b/test/test_arraylist.c
@@ -870,7 +870,7 @@ static void test_arraylist_iter(void)
         TEST_ASSERT_EQUAL_INT(data[i], temp);
         i--;
     }
-    TEST_ASSERT_EQUAL_INT(0, i);
+    TEST_ASSERT_EQUAL_INT(-1, i);
 
     arraylist_free(&arraylist);
 }
diff --git a/test/test_darray.c b/test/test_darray.c
index 629811f..1ded611 100644
--- a/test/test_darray.c
+++ b/test/test_darray.c
@@ -662,8 +662,10 @@ static void test_darray_iter(void)
         temp = *(int *)iter->next(iter);
         TEST_ASSERT_EQUAL_INT(data[i], temp);
         i--;
+
+        // darray->print_obj(&temp);
     }
-    TEST_ASSERT_EQUAL_INT(0, i);
+    TEST_ASSERT_EQUAL_INT(-1, i);
 
     darray_free(&darray);
 }
diff --git a/test/test_deque.c b/test/test_deque.c
index 5c8d18d..29e0630 100644
--- a/test/test_deque.c
+++ b/test/test_deque.c
@@ -375,7 +375,7 @@ static void test_deque_iter(void)
         TEST_ASSERT_EQUAL_INT(data[i], temp);
         i--;
     }
-    TEST_ASSERT_EQUAL_INT(0, i);
+    TEST_ASSERT_EQUAL_INT(-1, i);
 
     deque_free(&deque);
 }
diff --git a/test/test_ringbuf.c b/test/test_ringbuf.c
index cae7b2d..26c5eb4 100644
--- a/test/test_ringbuf.c
+++ b/test/test_ringbuf.c
@@ -511,8 +511,10 @@ static void test_ringbuf_iter(void)
         temp = *(int *)iter->next(iter);
         TEST_ASSERT_EQUAL_INT(data[i], temp);
         i--;
+
+        ringbuf->print_obj(&temp);
     }
-    TEST_ASSERT_EQUAL_INT(0, i);
+    TEST_ASSERT_EQUAL_INT(-1, i);
 
     ringbuf_free(&ringbuf);
 }
diff --git a/test/test_segarray.c b/test/test_segarray.c
index 04a77f8..0aa0162 100644
--- a/test/test_segarray.c
+++ b/test/test_segarray.c
@@ -489,7 +489,7 @@ static void test_segarray_iter(void)
         TEST_ASSERT_EQUAL_INT(data[i], temp);
         i--;
     }
-    TEST_ASSERT_EQUAL_INT(0, i);
+    TEST_ASSERT_EQUAL_INT(-1, i);
     log_info("iter-reverse cuccess!");
 
     segarray_free(&segarray);
diff --git a/test/test_ustring.c b/test/test_ustring.c
index 5495997..6cb1274 100644
--- a/test/test_ustring.c
+++ b/test/test_ustring.c
@@ -430,6 +430,47 @@ void test_ustring_count(void)
     ustring_free(&str);
 }
 
+static void test_ustring_iter(void)
+{
+    const char *data = "hello wolrd!";
+    ustring_t ustring = ustring_new(uv(data));
+
+    size_t i = 0;
+    char temp;
+    size_t len = ustring->len(ustring);
+
+    iterator_t iter = ustring->iter(ustring, LINEAR_FORWARD);
+    i = 0;
+    TEST_ASSERT_TRUE(iter->hasnext(iter));
+    while(iter->hasnext(iter))
+    {
+        temp = *(int *)iter->next(iter);
+        TEST_ASSERT_EQUAL_INT(data[i], temp);
+        i++;
+
+        // ustring->print_obj(&temp);
+    }
+    TEST_ASSERT_EQUAL_INT(len, i);
+
+    iter = ustring->iter(ustring, LINEAR_REVERSE);
+    i = 0;
+    size_t idx = len - 1;
+    TEST_ASSERT_TRUE(iter->hasnext(iter));
+    while(iter->hasnext(iter))
+    {
+        temp = *(int *)iter->next(iter);
+        
+        TEST_ASSERT_EQUAL_INT(data[idx], temp);
+        idx-=1;
+        i++;
+        ustring->print_obj(&temp);
+    }
+    TEST_ASSERT_EQUAL_INT(len, i);
+
+    ustring_free(&ustring);
+}
+
+
 void test_ustring(void)
 {
     UnitySetTestFile(__FILE__);
@@ -480,4 +521,6 @@ void test_ustring(void)
     RUN_TEST(test_ustring_substr);
     RUN_TEST(test_ustring_index);
     RUN_TEST(test_ustring_count);
+
+    RUN_TEST(test_ustring_iter);
 }