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;
}
}
