Varargs Value Collection
3
GOBJECT Library

# Varargs Value Collection

Converting varargs to generic values

## Synopsis

    #include <glib-object.h>
    #include <gobject/gvaluecollector.h>

    union               GTypeCValue;
    #define             G_VALUE_COLLECT                     (value, var_args, flags, __error)
    #define             G_VALUE_LCOPY                       (value, var_args, flags, __error)
    #define             G_VALUE_COLLECT_FORMAT_MAX_LENGTH

## Description

The macros in this section provide the varargs parsing support needed in variadic GObject functions such as `g_object_new()` or `g_object_set()`. They currently support the collection of integral types, floating point types and pointers.

## Details

### union GTypeCValue

    union GTypeCValue
    {
      gint     v_int;
      glong    v_long;
      gint64   v_int64;
      gdouble  v_double;
      gpointer v_pointer;
    };

A union holding one collected value.

### G_VALUE_COLLECT()

    #define             G_VALUE_COLLECT(value, var_args, flags, __error)

Collects a variable argument value from a va_list. We have to implement the varargs collection as a macro, because on some systems va_list variables cannot be passed by reference.

`value` :

  a GValue return location. `value` is supposed to be initialized according to the value type to be collected

`var_args` :

  the va_list variable; it may be evaluated multiple times

`flags` :

  flags which are passed on to the `collect_value()` function of the GTypeValueTable of `value`.

`__error` :

  a gchar** variable that will be modified to hold a `g_new()` allocated error messages if something fails

### G_VALUE_LCOPY()

    #define             G_VALUE_LCOPY(value, var_args, flags, __error)

Collects a value's variable argument locations from a va_list.

`value` :

  a GValue return location. `value` is supposed to be initialized according to the value type to be collected

`var_args` :

  the va_list variable; it may be evaluated multiple times

`flags` :

  flags which are passed on to the `lcopy_value()` function of the GTypeValueTable of `value`.

`__error` :

  a gchar** variable that will be modified to hold a `g_new()` allocated error messages if something fails

### G_VALUE_COLLECT_FORMAT_MAX_LENGTH

    #define	G_VALUE_COLLECT_FORMAT_MAX_LENGTH	(8)

The maximal number of GTypeCValues which can be collected for a single GValue.

## See Also

GValueTable