### Method

# GLib Regex replace_eval

since: 2.14

#### Declaration

    gchar*
    g_regex_replace_eval (
      const GRegex* regex,
      const gchar* string,
      gssize string_len,
      gint start_position,
      GRegexMatchFlags match_options,
      GRegexEvalCallback eval,
      gpointer user_data,
      GError** error
    )

#### Description

Replaces occurrences of the pattern in regex with the output of `eval` for that occurrence.

Setting `start_position` differs from just passing over a shortened string and setting `G_REGEX_MATCH_NOTBOL` in the case of a pattern that begins with any kind of lookbehind assertion, such as “\b”.

The following example uses `g_regex_replace_eval()` to replace multiple strings at once:

    static gboolean
    eval_cb (const GMatchInfo *info,
             GString          *res,
             gpointer          data)
    {
      gchar *match;
      gchar *r;

       match = g_match_info_fetch (info, 0);
       r = g_hash_table_lookup ((GHashTable *)data, match);
       g_string_append (res, r);
       g_free (match);

       return FALSE;
    }

    ...

    GRegex *reg;
    GHashTable *h;
    gchar *res;

    h = g_hash_table_new (g_str_hash, g_str_equal);

    g_hash_table_insert (h, "1", "ONE");
    g_hash_table_insert (h, "2", "TWO");
    g_hash_table_insert (h, "3", "THREE");
    g_hash_table_insert (h, "4", "FOUR");

    reg = g_regex_new ("1|2|3|4", G_REGEX_DEFAULT, G_REGEX_MATCH_DEFAULT, NULL);
    res = g_regex_replace_eval (reg, text, -1, 0, 0, eval_cb, h, NULL);
    g_hash_table_destroy (h);

    ...

Available since: 2.14

#### Parameters

`string`

  Type: An array of `gchar`

  String to perform matches against.

  The length of the array is specified in the `string_len` argument.
  The data is owned by the caller of the method.
  Each element is a NUL terminated UTF-8 string.

`string_len`

  Type: `gssize`

  The length of `string`, in bytes, or -1 if `string` is nul-terminated.

`start_position`

  Type: `gint`

  Starting index of the string to match, in bytes.

`match_options`

  Type: `GRegexMatchFlags`

  Options for the match.

`eval`

  Type: `GRegexEvalCallback`

  A function to call for each match.

`user_data`

  Type: `gpointer`

  User data to pass to the function.

  The argument can be `NULL`.
  The data is owned by the caller of the method.

`error`

  Type: `GError **`

  The return location for a recoverable error.

  The argument can be `NULL`.
  If the return location is not `NULL`, then you must initialize it to a `NULL` `GError*`.
  The argument will be left initialized to `NULL` by the method if there are no errors.
  In case of error, the argument will be set to a newly allocated `GError`; the caller will take ownership of the data, and be responsible for freeing it.

#### Return value

Type: `gchar*`

A newly allocated string containing the replacements.

The caller of the method takes ownership of the data, and is responsible for freeing it.
The value is a NUL terminated UTF-8 string.