这里的代码给出了int num的错误值，如果我输入的num是例如11，printf函数将输出0.但是如果我将静态加到int num，printf生成的输出是正确的。有人可以解释原因。如果我将第二个scanf的格式说明符设为％c，那么也可以正确打印int值。
img答案 0 :(得分：2)
此
char ch;
scanf("%d", &ch);
将调用未定义的行为，因为您使用的是整数格式，以将其存储在字符中。
答案 1 :(得分：2)
并非专门针对printf()，问题是由对scanf()的错误调用引起的。
引用C11，章节§7.21.6.2
[...]除非
*表示分配抑制，否则 转换结果放在下面第一个参数指向的对象中 尚未收到转换结果的format参数。如果是这个对象 没有合适的类型，或者无法表示转换结果 在对象中，行为是未定义的。
对于%d转换说明符，预期的参数类型为
d[....]相应的参数应该是指针 有符号整数。
但是，你所提供的只是指向char的指针。不匹配。 Undefined behavior
OTOH，%c转换说明符，
c匹配字段指定的字符序列 width （如果指令中没有字段宽度，则为1）。 如果不存在l长度修饰符，则相应的参数应为a 指向大小足以接受的字符数组的初始元素的指针 序列。没有添加空字符。
所以使用
scanf("%c",&ch);
是对的。或者，您也可以使用
scanf("%hhd",&ch); //char is signed
scanf("%hhu",&ch); //char is unsigned
答案 2 :(得分：1)
您观察到的很可能是因为第二个scanf错误（char工具大）格式说明符会覆盖num所在的自动变量内存。
使num静态将其移动到全局变量内存并且它（种类）有效，但它仍然是未定义的行为，某些内存已被覆盖，您可能需要付出代价稍后的。因此，唯一的选择是指定正确的格式说明符，如您所指出的那样%c。
答案 3 :(得分：0)
尝试添加<?php
/**
* Magento
*
* NOTICE OF LICENSE
*
* This source file is subject to the Open Software License (OSL 3.0)
* that is bundled with this package in the file LICENSE.txt.
* It is also available through the world-wide-web at this URL:
* http://opensource.org/licenses/osl-3.0.php
* If you did not receive a copy of the license and are unable to
* obtain it through the world-wide-web, please send an email
* to license@magentocommerce.com so we can send you a copy immediately.
*
* DISCLAIMER
*
* Do not edit or add to this file if you wish to upgrade Magento to newer
* versions in the future. If you wish to customize Magento for your
* needs please refer to http://www.magentocommerce.com for more information.
*
* @category Mage
* @package Mage_Catalog
* @copyright Copyright (c) 2013 Magento Inc. (http://www.magentocommerce.com)
* @license http://opensource.org/licenses/osl-3.0.php Open Software License (OSL 3.0)
*/
/**
* Product options text type block
*
* @category Mage
* @package Mage_Catalog
* @author Magento Core Team <core@magentocommerce.com>
*/
class Mage_Catalog_Block_Product_View_Options_Type_Select
extends Mage_Catalog_Block_Product_View_Options_Abstract
{
/**
* Return html for control element
*
* @return string
*/
public function getValuesHtml()
{
$_option = $this->getOption();
$configValue = $this->getProduct()->getPreconfiguredValues()->getData('options/' . $_option->getId());
$store = $this->getProduct()->getStore();
if ($_option->getType() == Mage_Catalog_Model_Product_Option::OPTION_TYPE_DROP_DOWN
|| $_option->getType() == Mage_Catalog_Model_Product_Option::OPTION_TYPE_MULTIPLE) {
$require = ($_option->getIsRequire()) ? ' required-entry' : '';
$extraParams = '';
$select = $this->getLayout()->createBlock('core/html_select')
->setData(array(
'id' => 'select_'.$_option->getId(),
'class' => $require.' product-custom-option'
));
if ($_option->getType() == Mage_Catalog_Model_Product_Option::OPTION_TYPE_DROP_DOWN) {
$select->setName('options['.$_option->getid().']');
// ->addOption('', $this->__('Please Select'));
} else {
$select->setName('options['.$_option->getid().'][]');
$select->setClass('multiselect'.$require.' product-custom-option');
}
// This is a very specific case for Ring Size
// $isMale = $isFemale = $hasNoPrice = false;
// foreach ($_option->getValues() as $_value) {
// if ($_value->getTitle() == 'I' && $_value->getPrice() == 0.0000) {
// $isFemale = true;
// }
// else if ($_value->getTitle() == 'M' && $_value->getPrice() == 0.0000) {
// $isMale = true;
// }
// if ($_value->getPrice() == 0.0000) {
// $hasNoPrice = true;
// }
// }
foreach ($_option->getValues() as $_value) {
$priceStr = $this->_formatPrice(array(
'is_percent' => ($_value->getPriceType() == 'percent'),
'pricing_value' => $_value->getPrice(($_value->getPriceType() == 'percent'))
), false);
$select->addOption(
$_value->getOptionTypeId(),
$_value->getTitle() . ' ' . $priceStr . '',
array('price' => $this->helper('core')->currencyByStore($_value->getPrice(true), $store, false))
);
// Set Default for the following cases:
// Ring Size for Men = T, Women = M
// Price for Custom Option is $0 and is the last, unless defaulted by Men or Women.
// if ($_value->getTitle() == 'M' && $isFemale) {
// $select->setValue($_value->getOptionTypeId());
// }
// else if ($_value->getTitle() == 'T' && $isMale) {
// $select->setValue($_value->getOptionTypeId());
// }
// else if ($_value->getPrice() == 0.0000 && $hasNoPrice && !$isFemale && !$isMale) {
// $select->setValue($_value->getOptionTypeId());
// }
//not sure about this line
if ($sku_code[0] == 'F') {
$select->setValue($configValue);
}
else if ($_value->getTitle() == 'M') {
$select->setValue($_value->getOptionTypeId());
}
else if ($_value->getTitle() == 'T') {
$select->setValue($_value->getOptionTypeId());
}
}
if ($_option->getType() == Mage_Catalog_Model_Product_Option::OPTION_TYPE_MULTIPLE) {
$extraParams = ' multiple="multiple"';
}
if (!$this->getSkipJsReloadPrice()) {
$extraParams .= ' onchange="opConfig.reloadPrice()"';
}
$select->setExtraParams($extraParams);
if ($configValue) {
$select->setValue($configValue);
}
return $select->getHtml();
}
if ($_option->getType() == Mage_Catalog_Model_Product_Option::OPTION_TYPE_RADIO
|| $_option->getType() == Mage_Catalog_Model_Product_Option::OPTION_TYPE_CHECKBOX
) {
$selectHtml = '<ul id="options-'.$_option->getId().'-list" class="options-list">';
$require = ($_option->getIsRequire()) ? ' validate-one-required-by-name' : '';
$arraySign = '';
switch ($_option->getType()) {
case Mage_Catalog_Model_Product_Option::OPTION_TYPE_RADIO:
$type = 'radio';
$class = 'radio';
if (!$_option->getIsRequire()) {
$selectHtml .= '<li><input type="radio" id="options_' . $_option->getId() . '" class="'
. $class . ' product-custom-option" name="options[' . $_option->getId() . ']"'
. ($this->getSkipJsReloadPrice() ? '' : ' onclick="opConfig.reloadPrice()"')
. ' value="" checked="checked" /><span class="label"><label for="options_'
. $_option->getId() . '">' . $this->__('None') . '</label></span></li>';
}
break;
case Mage_Catalog_Model_Product_Option::OPTION_TYPE_CHECKBOX:
$type = 'checkbox';
$class = 'checkbox';
$arraySign = '[]';
break;
}
$count = 1;
foreach ($_option->getValues() as $_value) {
$count++;
$priceStr = $this->_formatPrice(array(
'is_percent' => ($_value->getPriceType() == 'percent'),
'pricing_value' => $_value->getPrice($_value->getPriceType() == 'percent')
));
$htmlValue = $_value->getOptionTypeId();
if ($arraySign) {
$checked = (is_array($configValue) && in_array($htmlValue, $configValue)) ? 'checked' : '';
} else {
$checked = $configValue == $htmlValue ? 'checked' : '';
}
$selectHtml .= '<li>' . '<input type="' . $type . '" class="' . $class . ' ' . $require
. ' product-custom-option"'
. ($this->getSkipJsReloadPrice() ? '' : ' onclick="opConfig.reloadPrice()"')
. ' name="options[' . $_option->getId() . ']' . $arraySign . '" id="options_' . $_option->getId()
. '_' . $count . '" value="' . $htmlValue . '" ' . $checked . ' price="'
. $this->helper('core')->currencyByStore($_value->getPrice(true), $store, false) . '" />'
. '<span class="label"><label for="options_' . $_option->getId() . '_' . $count . '">'
. $_value->getTitle() . ' ' . $priceStr . '</label></span>';
if ($_option->getIsRequire()) {
$selectHtml .= '<script type="text/javascript">' . '$(\'options_' . $_option->getId() . '_'
. $count . '\').advaiceContainer = \'options-' . $_option->getId() . '-container\';'
. '$(\'options_' . $_option->getId() . '_' . $count
. '\').callbackFunction = \'validateOptionsCallback\';' . '</script>';
}
$selectHtml .= '</li>';
}
$selectHtml .= '</ul>';
return $selectHtml;
}
}
}
，例如\n。也许可以帮上忙。
如果您使用scanf("%d\n", &num);