source: trunk/www.guidonia.net/wp/wp-content/plugins/contact-form-7/modules/select.php@ 44

<?php
/**
** A base module for [select] and [select*]
**/

/* Shortcode handler */

function wpcf7_select_shortcode_handler( $tag ) {
        global $wpcf7_contact_form;

        if ( ! is_array( $tag ) )
                return '';

        $type = $tag['type'];
        $name = $tag['name'];
        $options = (array) $tag['options'];
        $values = (array) $tag['values'];

        if ( empty( $name ) )
                return '';

        $atts = '';
        $id_att = '';
        $class_att = '';

        $defaults = array();

        if ( 'select*' == $type )
                $class_att .= ' wpcf7-validates-as-required';

        foreach ( $options as $option ) {
                if ( preg_match( '%^id:([-0-9a-zA-Z_]+)$%', $option, $matches ) ) {
                        $id_att = $matches[1];

                } elseif ( preg_match( '%^class:([-0-9a-zA-Z_]+)$%', $option, $matches ) ) {
                        $class_att .= ' ' . $matches[1];

                } elseif ( preg_match( '/^default:([0-9_]+)$/', $option, $matches ) ) {
                        $defaults = explode( '_', $matches[1] );
                }
        }

        if ( $id_att )
                $atts .= ' id="' . trim( $id_att ) . '"';

        if ( $class_att )
                $atts .= ' class="' . trim( $class_att ) . '"';

        $multiple = (bool) preg_grep( '%^multiple$%', $options );
        $include_blank = (bool) preg_grep( '%^include_blank$%', $options );

        $empty_select = empty( $values );
        if ( $empty_select || $include_blank )
                array_unshift( $values, '---' );

        $html = '';

        $posted = is_a( $wpcf7_contact_form, 'WPCF7_ContactForm' ) && $wpcf7_contact_form->is_posted();

        foreach ( $values as $key => $value ) {
                $selected = false;

                if ( ! $empty_select && in_array( $key + 1, (array) $defaults ) )
                        $selected = true;

                if ( $posted ) {
                        if ( $multiple && in_array( esc_sql( $value ), (array) $_POST[$name] ) )
                                $selected = true;
                        if ( ! $multiple && $_POST[$name] == esc_sql( $value ) )
                                $selected = true;
                }

                $selected = $selected ? ' selected="selected"' : '';

                if ( is_array( $tag['labels'] ) && isset( $tag['labels'][$key] ) )
                        $label = $tag['labels'][$key];
                else
                        $label = $value;

                $html .= '<option value="' . esc_attr( $value ) . '"' . $selected . '>' . esc_html( $label ) . '</option>';
        }

        if ( $multiple )
                $atts .= ' multiple="multiple"';

        $html = '<select name="' . $name . ( $multiple ? '[]' : '' ) . '"' . $atts . '>' . $html . '</select>';

        $validation_error = '';
        if ( is_a( $wpcf7_contact_form, 'WPCF7_ContactForm' ) )
                $validation_error = $wpcf7_contact_form->validation_error( $name );

        $html = '<span class="wpcf7-form-control-wrap ' . $name . '">' . $html . $validation_error . '</span>';

        return $html;
}

wpcf7_add_shortcode( 'select', 'wpcf7_select_shortcode_handler', true );
wpcf7_add_shortcode( 'select*', 'wpcf7_select_shortcode_handler', true );


/* Validation filter */

function wpcf7_select_validation_filter( $result, $tag ) {
        global $wpcf7_contact_form;

        $type = $tag['type'];
        $name = $tag['name'];
        $values = $tag['values'];

        if ( is_array( $_POST[$name] ) ) {
                foreach ( $_POST[$name] as $key => $value ) {
                        $value = stripslashes( $value );
                        if ( ! in_array( $value, (array) $values ) ) // Not in given choices.
                                unset( $_POST[$name][$key] );
                }
        } else {
                $value = stripslashes( $_POST[$name] );
                if ( ! in_array( $value, (array) $values ) ) //  Not in given choices.
                        $_POST[$name] = '';
        }

        if ( 'select*' == $type ) {
                if ( empty( $_POST[$name] ) ||
                        ! is_array( $_POST[$name] ) && '---' == $_POST[$name] ||
                        is_array( $_POST[$name] ) && 1 == count( $_POST[$name] ) && '---' == $_POST[$name][0] ) {
                        $result['valid'] = false;
                        $result['reason'][$name] = $wpcf7_contact_form->message( 'invalid_required' );
                }
        }

        return $result;
}

add_filter( 'wpcf7_validate_select', 'wpcf7_select_validation_filter', 10, 2 );
add_filter( 'wpcf7_validate_select*', 'wpcf7_select_validation_filter', 10, 2 );

?>