1 files changed, 13 insertions, 7 deletions
diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index adf2a8de9a..3329310ab1 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -146,23 +146,29 @@ char *qstrcpy(char *dst, const char *src)
     A safe \c strncpy() function.
 
     Copies at most \a len bytes from \a src (stopping at \a len or the
-    terminating '\\0' whichever comes first) into \a dst and returns a
-    pointer to \a dst. Guarantees that \a dst is '\\0'-terminated. If
-    \a src or \a dst is \nullptr, returns \nullptr immediately.
+    terminating '\\0' whichever comes first) into \a dst. Guarantees that \a
+    dst is '\\0'-terminated, except when \a dst is \nullptr or \a len is 0. If
+    \a src is \nullptr, returns \nullptr, otherwise returns \a dst.
 
     This function assumes that \a dst is at least \a len characters
     long.
 
     \note If \a dst and \a src overlap, the behavior is undefined.
 
+    \note Unlike strncpy(), this function does \e not write '\\0' to all \a
+    len bytes of \a dst, but stops after the terminating '\\0'. In this sense,
+    it's similar to C11's strncpy_s().
+
     \sa qstrcpy()
 */
 
 char *qstrncpy(char *dst, const char *src, size_t len)
 {
-    if (!src || !dst)
-        return nullptr;
-    if (len > 0) {
+    if (dst && len > 0) {
+        if (!src) {
+            *dst = '\0';
+            return nullptr;
+        }
 #ifdef Q_CC_MSVC
         strncpy_s(dst, len, src, len - 1);
 #else
@@ -170,7 +176,7 @@ char *qstrncpy(char *dst, const char *src, size_t len)
 #endif
         dst[len-1] = '\0';
     }
-    return dst;
+    return src ? dst : nullptr;
 }
 
 /*! \fn size_t qstrlen(const char *str)