$a
= 0;
echo
"0 与 ''、 empty、null、false 之间的关系:"
;
if
(
$a
==
''
){
echo
"0 == '';"
;
}
else
{
echo
"0 != '';"
;
}
if
(trim(
$a
) ==
''
){
echo
"trim(0) == '';"
;
}
else
{
echo
"trim(0) != '';"
;
}
if
(
strval
(
$a
) ==
''
){
echo
"strval(0) == '';"
;
}
else
{
echo
"strval(0) != '';"
;
}
if
(
$a
===
''
){
echo
"0 === '';"
;
}
else
{
echo
"0 !=== '';"
;
}
if
(
empty
(
$a
)){
echo
"0 is empty;"
;
}
else
{
echo
"0 is not empty;"
;
}
if
(
is_null
(
$a
)){
echo
"0 is null;"
;
}
else
{
echo
"0 is not null;"
;
}
if
(
is_numeric
(
$a
)){
echo
"0 is numeric;"
;
}
else
{
echo
"0 is not numeric;"
;
}
if
(
is_string
(
$a
)){
echo
"0 is string;"
;
}
else
{
echo
"0 is not string;"
;
}
if
(!
$a
){
echo
"0 is false;"
;
}
else
{
echo
"0 is not false;"
;
}
$a
=
''
;
echo
"'' 和 0、empty、null、false 之间的关系:"
;
if
(
$a
== 0){
echo
"'' == 0;"
;
}
else
{
echo
"'' != 0;"
;
}
if
(
intval
(
$a
) == 0){
echo
"intval('') == 0;"
;
}
else
{
echo
"intval('') != 0;"
;
}
if
(
empty
(
$a
)){
echo
"'' is empty;"
;
}
else
{
echo
"'' is not empty;"
;
}
if
(
is_null
(
$a
)){
echo
"'' is null;"
;
}
else
{
echo
"'' is not null;"
;
}
if
(
is_numeric
(
$a
)){
echo
"'' is numeric;"
;
}
else
{
echo
"'' is not numeric;"
;
}
if
(
is_string
(
$a
)){
echo
"'' is string;"
;
}
else
{
echo
"'' is not string;"
;
}
if
(!
$a
){
echo
"'' is false;"
;
}
else
{
echo
"'' is not false;"
;
}
$a
= null;
echo
"null 和 ''、0、empty、false 之间的关系:"
;
if
(
$a
==
''
){
echo
"null == '';"
;
}
else
{
echo
"null != '';"
;
}
if
(
$a
== 0){
echo
"null == 0;"
;
}
else
{
echo
"null != 0;"
;
}
if
(
$a
===
''
){
echo
"null === '';"
;
}
else
{
echo
"null !=== '';"
;
}
if
(
$a
=== 0){
echo
"null === 0;"
;
}
else
{
echo
"null !=== 0;"
;
}
if
(
strval
(
$a
) ==
''
){
echo
"strval(null) == '';"
;
}
else
{
echo
"strval(null) != '';"
;
}
if
(
intval
(
$a
) == 0){
echo
"intval(null) == 0;"
;
}
else
{
echo
"intval(null) != 0;"
;
}
if
(
empty
(
$a
)){
echo
"null is empty;"
;
}
else
{
echo
"null is not empty;"
;
}
if
(
is_numeric
(
$a
)){
echo
"null is numeric;"
;
}
else
{
echo
"null is not numeric;"
;
}
if
(
is_string
(
$a
)){
echo
"null is string;"
;
}
else
{
echo
"null is not string;"
;
}
if
(!
$a
){
echo
"null is false;"
;
}
else
{
echo
"null is not false;"
;
}
echo
""
;