fix UB that cause warning

common/iovector.h

@@ -34,6 +34,7 @@ limitations under the License.
 #include <cstring>
 #include <new>
 #include <memory>
+#include <array>
 #include <sys/uio.h>
 
 #include <photon/common/callback.h>
@@ -308,22 +309,22 @@ class iovector
     struct iovec* begin()
     {
         do_assert();
-        return iovs + iov_begin;
+        return iovs.begin() + iov_begin;
     }
     const struct iovec* begin() const
     {
         do_assert();
-        return iovs + iov_begin;
+        return iovs.begin() + iov_begin;
     }
     struct iovec* end()
     {
         do_assert();
-        return iovs + iov_end;
+        return iovs.begin() + iov_end;
     }
     const struct iovec* end() const
     {
         do_assert();
-        return iovs + iov_end;
+        return iovs.begin() + iov_end;
     }
     struct iovec& operator[] (int64_t i)
     {
@@ -791,7 +792,7 @@ class iovector
     }
 
     void update(iovector_view va) {
-        iov_begin = va.iov - iovs;
+        iov_begin = va.iov - iovs.begin();
         iov_end = iov_begin + va.iovcnt;
     }
 
@@ -827,7 +828,7 @@ class iovector
     uint16_t capacity;              // total capacity
     uint16_t iov_begin, iov_end;    // [iov_begin, iov_end)
     uint16_t nbases;                // # of allocated pointers
-    struct iovec iovs[0];
+    std::array<struct iovec, 0> iovs;
 
     friend iovector* new_iovector(uint16_t capacity, uint16_t preserve);
     friend void delete_iovector(iovector* ptr);
@@ -841,7 +842,7 @@ class iovector
 
     inline __attribute__((always_inline))
     struct iovec* iovs_ptr() const {
-        return const_cast<struct iovec*>(iovs);
+        return const_cast<struct iovec*>(iovs.begin());
     }
 
     // not allowed to freely construct / destruct
@@ -861,7 +862,7 @@ class iovector
 
     struct IOVAllocation_ : public IOAlloc
     {
-        void* bases[0];
+        void* bases[];
         void* do_allocate(int size, uint16_t& nbases, uint16_t capacity)
         {
             return do_allocate(size, size, nbases, capacity);
@@ -936,7 +937,7 @@ template<uint16_t CAPACITY, uint16_t DEF_PRESERVE>
 class IOVectorEntity : public iovector
 {
 public:
-    struct iovec iovs[CAPACITY]; // same address with iovector::iovs
+    std::array<struct iovec, CAPACITY> iovs; // same address with iovector::iovs
     struct IOAlloc allocator;
     void* bases[CAPACITY];       // same address with IOVAllocation::bases