[gnc-glib-utils] gnc_g_list_stringjoin to join a GList of strings

It traverses the GList twice (once to calculate the length) but
allocates only once.

Includes snippet from
https://www.joelonsoftware.com/2001/12/11/back-to-basics/

libgnucash/core-utils/gnc-glib-utils.c

@@ -327,3 +327,35 @@ void gnc_gpid_kill(GPid pid)
     }
 #endif /* G_OS_WIN32 */
 }
+
+static inline char*
+gnc_strcat (char* dest, const char* src)
+{
+    while (*dest) dest++;
+    while ((*dest++ = *src++));
+    return --dest;
+}
+
+gchar *
+gnc_g_list_stringjoin (GList *list_of_strings, const gchar *sep)
+{
+    gint seplen = sep ? strlen(sep) : 0;
+    gint length = -seplen;
+    gchar *retval, *p;
+
+    if (!list_of_strings)
+        return NULL;
+
+    for (GList *n = list_of_strings; n; n = n->next)
+        length += strlen ((gchar*)n->data) + seplen;
+
+    p = retval = (gchar*) g_malloc0 (length * sizeof (gchar) + 1);
+    for (GList *n = list_of_strings; n; n = n->next)
+    {
+        p = gnc_strcat (p, (gchar*)n->data);
+        if (n->next && sep)
+            p = gnc_strcat (p, sep);
+    }
+
+    return retval;
+}

libgnucash/core-utils/gnc-glib-utils.h

@@ -183,6 +183,22 @@ void gnc_scm_log_debug(const gchar *msg);
  @{
 */
 
+
+/**
+ * @brief Return a string joining a GList whose elements are gchar*
+ * strings. Returns NULL if an empty GList* is passed through. The
+ * optional sep string will be used as separator. Must be g_freed when
+ * not needed anymore.
+ *
+ * @param list_of_strings A GList of chars*
+ *
+ * @param sep a separator or NULL
+ *
+ * @return A newly allocated string that has to be g_free'd by the
+ * caller.
+ **/
+gchar * gnc_g_list_stringjoin (GList *list_of_strings, const gchar *sep);
+
 /** Kill a process.  On UNIX send a SIGKILL, on Windows call TerminateProcess.
  *
  *  @param pid The process ID. */

libgnucash/core-utils/test/test-gnc-glib-utils.c

@@ -53,6 +53,62 @@ test_gnc_utf8_strip_invalid_and_controls (gconstpointer data)
     g_free (msg1);
 }
 
+static void
+test_g_list_stringjoin (gconstpointer data)
+{
+    GList *test = NULL;
+    gchar *ret;
+
+    ret = gnc_g_list_stringjoin (NULL, NULL);
+    g_assert (ret == NULL);
+
+    ret = gnc_g_list_stringjoin (NULL, ":");
+    g_assert (ret == NULL);
+
+    test = g_list_prepend (test, "one");
+
+    ret = gnc_g_list_stringjoin (test, NULL);
+    g_assert_cmpstr (ret, ==, "one");
+    g_free (ret);
+
+    ret = gnc_g_list_stringjoin (test, "");
+    g_assert_cmpstr (ret, ==, "one");
+    g_free (ret);
+
+    ret = gnc_g_list_stringjoin (test, ":");
+    g_assert_cmpstr (ret, ==, "one");
+    g_free (ret);
+
+    test = g_list_prepend (test, "two");
+
+    ret = gnc_g_list_stringjoin (test, NULL);
+    g_assert_cmpstr (ret, ==, "twoone");
+    g_free (ret);
+
+    ret = gnc_g_list_stringjoin (test, "");
+    g_assert_cmpstr (ret, ==, "twoone");
+    g_free (ret);
+
+    ret = gnc_g_list_stringjoin (test, ":");
+    g_assert_cmpstr (ret, ==, "two:one");
+    g_free (ret);
+
+    test = g_list_prepend (test, "three");
+
+    ret = gnc_g_list_stringjoin (test, NULL);
+    g_assert_cmpstr (ret, ==, "threetwoone");
+    g_free (ret);
+
+    ret = gnc_g_list_stringjoin (test, "");
+    g_assert_cmpstr (ret, ==, "threetwoone");
+    g_free (ret);
+
+    ret = gnc_g_list_stringjoin (test, ":");
+    g_assert_cmpstr (ret, ==, "three:two:one");
+    g_free (ret);
+
+    g_list_free (test);
+}
 
 int
 main (int argc, char *argv[])
@@ -62,6 +118,7 @@ main (int argc, char *argv[])
     g_test_init (&argc, &argv, NULL); // initialize test program
     g_test_add_data_func ("/core-utils/gnc_utf8_strip_invalid_and_controls invalid utf8", (gconstpointer)invalid_utf8, test_gnc_utf8_strip_invalid_and_controls);
     g_test_add_data_func ("/core-utils/gnc_utf8_strip_invalid_and_controls control chars", (gconstpointer)controls, test_gnc_utf8_strip_invalid_and_controls);
+    g_test_add_data_func ("/core-utils/gnc_g_list_stringjoin", NULL, test_g_list_stringjoin);
 
     return g_test_run();
 }