Various changes and improvements

- Replaced int by specific, more meaningful error codes.
- C99 states realloc can be safely called using NULL pointers.
- New function dynstr_dup().

dynstr.c

@@ -26,7 +26,7 @@ void dynstr_init(struct dynstr *const d)
     memset(d, 0, sizeof *d);
 }
 
-int dynstr_append(struct dynstr *const d, const char *const format, ...)
+enum dynstr_err dynstr_append(struct dynstr *const d, const char *const format, ...)
 {
     va_list ap;
 
@@ -34,19 +34,10 @@ int dynstr_append(struct dynstr *const d, const char *const format, ...)
 
     {
         const size_t src_len = vsnprintf(NULL, 0, format, ap);
-        size_t new_len;
+        const size_t new_len = d->len + src_len + 1;
         va_end(ap);
 
-        if (!d->str)
-        {
-            new_len = src_len + 1;
-            d->str = malloc(new_len * sizeof *d->str);
-        }
-        else
-        {
-            new_len = d->len + src_len + 1;
-            d->str = realloc(d->str, new_len * sizeof *d->str);
-        }
+        d->str = realloc(d->str, new_len * sizeof *d->str);
 
         if (d->str)
         {
@@ -57,11 +48,43 @@ int dynstr_append(struct dynstr *const d, const char *const format, ...)
         }
         else
         {
-            return 1;
+            return DYNSTR_ERR_ALLOC;
         }
     }
 
-    return 0;
+    return DYNSTR_OK;
+}
+
+enum dynstr_err dynstr_dup(struct dynstr *const dst, const struct dynstr *const src)
+{
+    if (!dst->str && !dst->len)
+    {
+        if (src->len && src->str)
+        {
+            const size_t sz = (src->len + 1) * sizeof *dst->str;
+            dst->str = realloc(dst->str, sz);
+
+            if (dst->str)
+            {
+                memcpy(dst->str, src->str, sz);
+                dst->len = src->len;
+            }
+            else
+            {
+                return DYNSTR_ERR_ALLOC;
+            }
+        }
+        else
+        {
+            return DYNSTR_ERR_SRC;
+        }
+    }
+    else
+    {
+        return DYNSTR_ERR_INIT;
+    }
+
+    return DYNSTR_OK;
 }
 
 void dynstr_free(struct dynstr *const d)

include/dynstr.h

@@ -45,7 +45,7 @@
 /**
  * Convenience macro that calls dynstr_append and returns its error code if failed.
  */
-#define dynstr_append_or_ret(d, format, ...) {const int err = dynstr_append(d, format, ## __VA_ARGS__); if (err) return err;}
+#define dynstr_append_or_ret(d, format, ...) {const enum dynstr_err err = dynstr_append(d, format, ## __VA_ARGS__); if (err) return err;}
 
 /**
  * Convenience macro that calls dynstr_append and returns zero if failed.
@@ -65,6 +65,19 @@ struct dynstr
     size_t len; /**< String length, null character not included. */
 };
 
+/**
+ * List of errors that this library might return.
+ * @note If using GNU C extensions, this errors can be translated into other
+ * types by using the convenience macros above.
+ */
+enum dynstr_err
+{
+   DYNSTR_OK, /**< Operation was successful. */
+   DYNSTR_ERR_ALLOC, /**< Alloc operation failed. */
+   DYNSTR_ERR_INIT, /**< Dynamic string was not initialized. */
+   DYNSTR_ERR_SRC /**< Source string has invalid parameters. */
+};
+
 /**
  * Reportedly, it initializes an empty string with zero length.
  * @attention Always call this function when creating a dynstr instance.
@@ -78,9 +91,25 @@ void dynstr_init(struct dynstr *d);
  * dynamic string.
  * @param d Dynamic string where new string will be appended.
  * @param format String literal in printf format.
- * @return Returns 0 if successful, 1 if alloc operation failed.
+ * @return Returns one of the following error codes:
+ *    # DYNSTR_OK if successful.
+ *    # DYNSTR_ERR_ALLOC if no more memory is available.
  */
-int dynstr_append(struct dynstr *d, const char *format, ...);
+enum dynstr_err dynstr_append(struct dynstr *d, const char *format, ...);
+
+/**
+ * This function duplicates a dynamic string to another instance.
+ * @attention Destination instance must be initialized before calling
+ * this function.
+ * @attention Since this function performs a deep copy, please remember to
+ * free the source instance if no longer used to avoid memory leaks.
+ * @return Returns one of the following error codes:
+ *    # DYNSTR_OK if successful.
+ *    # DYNSTR_ERR_ALLOC if no more memory is available.
+ *    # DYNSTR_ERR_INIT if destination dynamic string was not initialized.
+ *    # DYNSTR_ERR_SRC if source dynamic string has no length or data.
+ */
+enum dynstr_err dynstr_dup(struct dynstr *dst, const struct dynstr *src);
 
 /**
  * This function frees memory used by the dynamic string.