几道无聊的php的比较运算题，有兴趣的玩一玩

趣题:
下面的几段代码分别输出true or false？

第一个：

<?php
$key=1;
var_dump($key == " \t01ab");
?>

第二个：

<?php
$key='1';
var_dump($key == " \t01ab");
?>

第三个：

<?php
$key=0;
var_dump($key == " \t01ab");
?>

第四个：

<?php
$key=0;
var_dump($key == " \t00ab");
?>

第五个：

<?php
$key=0;
var_dump($key == " ab");
?>

第六个：

<?php
$key='0';
var_dump($key == " ab");
?>

答案：
第一道：true

第二道：false

第三道：false

第四道：true

第五道：true

第六道：false

题解：
当比较的一方是数字时，字符串会转换成数字，然后再进行比较。

如果比较的两方全部为字符串时，当然就不存在转换，只是单纯的进行字符串比较了。

需要注意的是，字符串转换成数字时，如果字符串被视为十进制格式时，大概的转换规则如下：

1.过滤前面的一些字符。这些字符包括空格，'\t' ，'\n' ， '\r' ，'\v' ， '\f' 和 0

2.把后面不是数字的字符和之后字符也过滤掉。如 123abc4 就会把a和之后的字符过滤掉。

思考题:
如果前面的== 改成 === 结果如何？
下面的代码输出true or false？

<?PHP
$a = 0;
if(in_array($a, array('index', 'post'))){
    echo "true";
}else{
    echo "false";
}
?>

进阶：
以上只是大概的转换规则，可能有说的不严谨的地方。具体的规则大家可以查看源码：

zend/zend_operators.c:1402行
这个方法说明了比较时，各种情况下比较规则。

ZEND_API int compare_function(zval *result, zval *op1, zval *op2 TSRMLS_DC) /* {{{ */
{
	int ret;
	int converted = 0;
	zval op1_copy, op2_copy;
	zval *op_free;

	while (1) {
		switch (TYPE_PAIR(Z_TYPE_P(op1), Z_TYPE_P(op2))) {
			case TYPE_PAIR(IS_LONG, IS_LONG):
				ZVAL_LONG(result, Z_LVAL_P(op1)>Z_LVAL_P(op2)?1:(Z_LVAL_P(op1)<Z_LVAL_P(op2)?-1:0));
				return SUCCESS;

			case TYPE_PAIR(IS_DOUBLE, IS_LONG):
				Z_DVAL_P(result) = Z_DVAL_P(op1) - (double)Z_LVAL_P(op2);
				ZVAL_LONG(result, ZEND_NORMALIZE_BOOL(Z_DVAL_P(result)));
				return SUCCESS;

			case TYPE_PAIR(IS_LONG, IS_DOUBLE):
				Z_DVAL_P(result) = (double)Z_LVAL_P(op1) - Z_DVAL_P(op2);
				ZVAL_LONG(result, ZEND_NORMALIZE_BOOL(Z_DVAL_P(result)));
				return SUCCESS;

			case TYPE_PAIR(IS_DOUBLE, IS_DOUBLE):
				if (Z_DVAL_P(op1) == Z_DVAL_P(op2)) {
					ZVAL_LONG(result, 0);
				} else {
					Z_DVAL_P(result) = Z_DVAL_P(op1) - Z_DVAL_P(op2);
					ZVAL_LONG(result, ZEND_NORMALIZE_BOOL(Z_DVAL_P(result)));
				}
				return SUCCESS;

			case TYPE_PAIR(IS_ARRAY, IS_ARRAY):
				zend_compare_arrays(result, op1, op2 TSRMLS_CC);
				return SUCCESS;

			case TYPE_PAIR(IS_NULL, IS_NULL):
				ZVAL_LONG(result, 0);
				return SUCCESS;

			case TYPE_PAIR(IS_NULL, IS_BOOL):
				ZVAL_LONG(result, Z_LVAL_P(op2) ? -1 : 0);
				return SUCCESS;

			case TYPE_PAIR(IS_BOOL, IS_NULL):
				ZVAL_LONG(result, Z_LVAL_P(op1) ? 1 : 0);
				return SUCCESS;

			case TYPE_PAIR(IS_BOOL, IS_BOOL):
				ZVAL_LONG(result, ZEND_NORMALIZE_BOOL(Z_LVAL_P(op1) - Z_LVAL_P(op2)));
				return SUCCESS;

			case TYPE_PAIR(IS_STRING, IS_STRING):
				zendi_smart_strcmp(result, op1, op2);
				return SUCCESS;

			case TYPE_PAIR(IS_NULL, IS_STRING):
				ZVAL_LONG(result, zend_binary_strcmp("", 0, Z_STRVAL_P(op2), Z_STRLEN_P(op2)));
				return SUCCESS;

			case TYPE_PAIR(IS_STRING, IS_NULL):
				ZVAL_LONG(result, zend_binary_strcmp(Z_STRVAL_P(op1), Z_STRLEN_P(op1), "", 0));
				return SUCCESS;

			case TYPE_PAIR(IS_OBJECT, IS_NULL):
				ZVAL_LONG(result, 1);
				return SUCCESS;

			case TYPE_PAIR(IS_NULL, IS_OBJECT):
				ZVAL_LONG(result, -1);
				return SUCCESS;

			case TYPE_PAIR(IS_OBJECT, IS_OBJECT):
				/* If both are objects sharing the same comparision handler then use is */
				if (Z_OBJ_HANDLER_P(op1,compare_objects) == Z_OBJ_HANDLER_P(op2,compare_objects)) {
					if (Z_OBJ_HANDLE_P(op1) == Z_OBJ_HANDLE_P(op2)) {
						/* object handles are identical, apparently this is the same object */
						ZVAL_LONG(result, 0);
						return SUCCESS;
					}
					ZVAL_LONG(result, Z_OBJ_HT_P(op1)->compare_objects(op1, op2 TSRMLS_CC));
					return SUCCESS;
				}
				/* break missing intentionally */

			default:
				if (Z_TYPE_P(op1) == IS_OBJECT) {
					if (Z_OBJ_HT_P(op1)->get) {
						op_free = Z_OBJ_HT_P(op1)->get(op1 TSRMLS_CC);
						ret = compare_function(result, op_free, op2 TSRMLS_CC);
						zend_free_obj_get_result(op_free TSRMLS_CC);
						return ret;
					} else if (Z_TYPE_P(op2) != IS_OBJECT && Z_OBJ_HT_P(op1)->cast_object) {
						ALLOC_INIT_ZVAL(op_free);
						if (Z_OBJ_HT_P(op1)->cast_object(op1, op_free, Z_TYPE_P(op2) TSRMLS_CC) == FAILURE) {
							ZVAL_LONG(result, 1);
							zend_free_obj_get_result(op_free TSRMLS_CC);
							return SUCCESS;
						}
						ret = compare_function(result, op_free, op2 TSRMLS_CC);
						zend_free_obj_get_result(op_free TSRMLS_CC);
						return ret;
					}
				}
				if (Z_TYPE_P(op2) == IS_OBJECT) {
					if (Z_OBJ_HT_P(op2)->get) {
						op_free = Z_OBJ_HT_P(op2)->get(op2 TSRMLS_CC);
						ret = compare_function(result, op1, op_free TSRMLS_CC);
						zend_free_obj_get_result(op_free TSRMLS_CC);
						return ret;
					} else if (Z_TYPE_P(op1) != IS_OBJECT && Z_OBJ_HT_P(op2)->cast_object) {
						ALLOC_INIT_ZVAL(op_free);
						if (Z_OBJ_HT_P(op2)->cast_object(op2, op_free, Z_TYPE_P(op1) TSRMLS_CC) == FAILURE) {
							ZVAL_LONG(result, -1);
							zend_free_obj_get_result(op_free TSRMLS_CC);
							return SUCCESS;
						}
						ret = compare_function(result, op1, op_free TSRMLS_CC);
						zend_free_obj_get_result(op_free TSRMLS_CC);
						return ret;
					} else if (Z_TYPE_P(op1) == IS_OBJECT) {
						ZVAL_LONG(result, 1);
						return SUCCESS;
					}
				}
				if (!converted) {
					if (Z_TYPE_P(op1) == IS_NULL) {
						zendi_convert_to_boolean(op2, op2_copy, result);
						ZVAL_LONG(result, Z_LVAL_P(op2) ? -1 : 0);
						return SUCCESS;
					} else if (Z_TYPE_P(op2) == IS_NULL) {
						zendi_convert_to_boolean(op1, op1_copy, result);
						ZVAL_LONG(result, Z_LVAL_P(op1) ? 1 : 0);
						return SUCCESS;
					} else if (Z_TYPE_P(op1) == IS_BOOL) {
						zendi_convert_to_boolean(op2, op2_copy, result);
						ZVAL_LONG(result, ZEND_NORMALIZE_BOOL(Z_LVAL_P(op1) - Z_LVAL_P(op2)));
						return SUCCESS;
					} else if (Z_TYPE_P(op2) == IS_BOOL) {
						zendi_convert_to_boolean(op1, op1_copy, result);
						ZVAL_LONG(result, ZEND_NORMALIZE_BOOL(Z_LVAL_P(op1) - Z_LVAL_P(op2)));
						return SUCCESS;
					} else {
						zendi_convert_scalar_to_number(op1, op1_copy, result);
						zendi_convert_scalar_to_number(op2, op2_copy, result);
						converted = 1;
					}
				} else if (Z_TYPE_P(op1)==IS_ARRAY) {
					ZVAL_LONG(result, 1);
					return SUCCESS;
				} else if (Z_TYPE_P(op2)==IS_ARRAY) {
					ZVAL_LONG(result, -1);
					return SUCCESS;
				} else if (Z_TYPE_P(op1)==IS_OBJECT) {
					ZVAL_LONG(result, 1);
					return SUCCESS;
				} else if (Z_TYPE_P(op2)==IS_OBJECT) {
					ZVAL_LONG(result, -1);
					return SUCCESS;
				} else {
					ZVAL_LONG(result, 0);
					return FAILURE;
				}
		}
	}
}
/* }}} */

zend/zend_operators.c:132行
字符串转换数字是，前面字符过滤规则

static inline zend_uchar is_numeric_string_ex(const char *str, int length, long *lval, double *dval, int allow_errors, int *oflow_info)
{
	const char *ptr;
	int base = 10, digits = 0, dp_or_e = 0;
	double local_dval;
	zend_uchar type;

	if (!length) {
		return 0;
	}

	if (oflow_info != NULL) {
		*oflow_info = 0;
	}

	/* Skip any whitespace
	 * This is much faster than the isspace() function */
	while (*str == ' ' || *str == '\t' || *str == '\n' || *str == '\r' || *str == '\v' || *str == '\f') {
		str++;
		length--;
	}
	ptr = str;

	if (*ptr == '-' || *ptr == '+') {
		ptr++;
	}

	if (ZEND_IS_DIGIT(*ptr)) {
		/* Handle hex numbers
		 * str is used instead of ptr to disallow signs and keep old behavior */
		if (length > 2 && *str == '0' && (str[1] == 'x' || str[1] == 'X')) {
			base = 16;
			ptr += 2;
		}

		/* Skip any leading 0s */
		while (*ptr == '0') {
			ptr++;
		}

		/* Count the number of digits. If a decimal point/exponent is found,
		 * it's a double. Otherwise, if there's a dval or no need to check for
		 * a full match, stop when there are too many digits for a long */
		for (type = IS_LONG; !(digits >= MAX_LENGTH_OF_LONG && (dval || allow_errors == 1)); digits++, ptr++) {
check_digits:
			if (ZEND_IS_DIGIT(*ptr) || (base == 16 && ZEND_IS_XDIGIT(*ptr))) {
				continue;
			} else if (base == 10) {
				if (*ptr == '.' && dp_or_e < 1) {
					goto process_double;
				} else if ((*ptr == 'e' || *ptr == 'E') && dp_or_e < 2) {
					const char *e = ptr + 1;

					if (*e == '-' || *e == '+') {
						ptr = e++;
					}
					if (ZEND_IS_DIGIT(*e)) {
						goto process_double;
					}
				}
			}

			break;
		}

		if (base == 10) {
			if (digits >= MAX_LENGTH_OF_LONG) {
				if (oflow_info != NULL) {
					*oflow_info = *str == '-' ? -1 : 1;
				}
				dp_or_e = -1;
				goto process_double;
			}
		} else if (!(digits < SIZEOF_LONG * 2 || (digits == SIZEOF_LONG * 2 && ptr[-digits] <= '7'))) {
			if (dval) {
				local_dval = zend_hex_strtod(str, &ptr);
			}
			if (oflow_info != NULL) {
				*oflow_info = 1;
			}
			type = IS_DOUBLE;
		}
	} else if (*ptr == '.' && ZEND_IS_DIGIT(ptr[1])) {
process_double:
		type = IS_DOUBLE;

		/* If there's a dval, do the conversion; else continue checking
		 * the digits if we need to check for a full match */
		if (dval) {
			local_dval = zend_strtod(str, &ptr);
		} else if (allow_errors != 1 && dp_or_e != -1) {
			dp_or_e = (*ptr++ == '.') ? 1 : 2;
			goto check_digits;
		}
	} else {
		return 0;
	}

	if (ptr != str + length) {
		if (!allow_errors) {
			return 0;
		}
		if (allow_errors == -1) {
			zend_error(E_NOTICE, "A non well formed numeric value encountered");
		}
	}

	if (type == IS_LONG) {
		if (digits == MAX_LENGTH_OF_LONG - 1) {
			int cmp = strcmp(&ptr[-digits], long_min_digits);

			if (!(cmp < 0 || (cmp == 0 && *str == '-'))) {
				if (dval) {
					*dval = zend_strtod(str, NULL);
				}
				if (oflow_info != NULL) {
					*oflow_info = *str == '-' ? -1 : 1;
				}

				return IS_DOUBLE;
			}
		}

		if (lval) {
			*lval = strtol(str, NULL, base);
		}

		return IS_LONG;
	} else {
		if (dval) {
			*dval = local_dval;
		}

		return IS_DOUBLE;
	}
}

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原文链接：几道无聊的php的比较运算题，有兴趣的玩一玩，转载请注明来源！

4 条评论

周梦康 2014 年 4 月 24 日下午 10:12

这种题目真的会有人考么？我严重怀疑。。。

回复
1. 信海龙_ 管理员 2014 年 4 月 26 日上午 9:53
  
  学习不仅仅是为了考试。其实是为了应用。之所以写这篇文章是因为有个同事项目开发过程中遇到了这个坑，问到我。为了避免大家再次埰坑才写的。
  
  回复
  1. 周梦康 2014 年 4 月 28 日上午 11:27
    
    说的是。不好意思，我看到标题中“php*题”，我看成“面试题”了。
    
    回复
  2. 周梦康 2014 年 4 月 28 日上午 11:28
    
    博客内容很赞，获益匪浅，希望楼主常更新哦！
    
    回复

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