diff --git a/include/common/standard.h b/include/common/standard.h
index 065a4fd..5dcb6c7 100644
--- a/include/common/standard.h
+++ b/include/common/standard.h
@@ -668,4 +668,33 @@
  */
 char *gmt2str_log(char *dst, struct tm *tm, size_t size);
 
+/* Dynamically allocates a string of the proper length to hold the formatted
+ * output. NULL is returned on error. The caller is responsible for freeing the
+ * memory area using free(). The resulting string is returned in <out> if the
+ * pointer is not NULL. A previous version of <out> might be used to build the
+ * new string, and it will be freed before returning if it is not NULL, which
+ * makes it possible to build complex strings from iterative calls without
+ * having to care about freeing intermediate values, as in the example below :
+ *
+ *     memprintf(&err, "invalid argument: '%s'", arg);
+ *     ...
+ *     memprintf(&err, "parser said : <%s>\n", *err);
+ *     ...
+ *     free(*err);
+ *
+ * This means that <err> must be initialized to NULL before first invocation.
+ * The return value also holds the allocated string, which eases error checking
+ * and immediate consumption. If the output pointer is not used, NULL must be
+ * passed instead and it will be ignored.
+ *
+ * It is also convenient to use it without any free except the last one :
+ *    err = NULL;
+ *    if (!fct1(err)) report(*err);
+ *    if (!fct2(err)) report(*err);
+ *    if (!fct3(err)) report(*err);
+ *    free(*err);
+ */
+char *memprintf(char **out, const char *format, ...)
+	__attribute__ ((format(printf, 2, 3)));
+
 #endif /* _COMMON_STANDARD_H */