diff -r cf19b7820ff0 -r 94360453bce4 src/cx/string.h
--- a/src/cx/string.h	Thu Dec 25 12:07:37 2025 +0100
+++ b/src/cx/string.h	Sun Dec 28 14:10:14 2025 +0100
@@ -41,6 +41,9 @@
 
 #include <string.h>
 
+/** Convenience macro for creating a null string */
+#define CX_NULLSTR cx_mutstr(NULL)
+
 /** Expands a UCX string as printf arguments. */
 #define CX_SFMT(s) (int) (s).length, (s).ptr
 
@@ -419,17 +422,17 @@
  * @note It is guaranteed that there is only one allocation for the
  * resulting string.
  * It is also guaranteed that the returned string is zero-terminated.
+ * If allocation fails, the @c ptr in the returned string will be @c NULL.
  *
  * @param alloc the allocator to use
  * @param str   the string the other strings shall be concatenated to
  * @param count the number of the other following strings to concatenate
  * @param ...   all other UCX strings
- * @retval zero success
- * @retval non-zero allocation failure
+ * @return the concatenated string
  */
 cx_attr_nonnull
-CX_EXPORT int cx_strcat_a(const CxAllocator *alloc,
-        cxmutstr *str, size_t count, ...);
+CX_EXPORT cxmutstr cx_strcat_a(const CxAllocator *alloc,
+        cxmutstr str, size_t count, ...);
 
 /**
  * Concatenates strings and returns a new string.
@@ -440,12 +443,12 @@
  * @note It is guaranteed that there is only one allocation for the
  * resulting string.
  * It is also guaranteed that the returned string is zero-terminated.
+ * If allocation fails, the @c ptr in the returned string will be @c NULL.
  *
  * @param str (@c cxmutstr*) the string the other strings shall be concatenated to
  * @param count (@c size_t) the number of the other following strings to concatenate
  * @param ... all other UCX strings
- * @retval zero success
- * @retval non-zero allocation failure
+ * @return the concatenated string
  */
 #define cx_strcat(str, count, ...) \
         cx_strcat_a(cxDefaultAllocator, str, count, __VA_ARGS__)