会导致 Unexpected else 语法错误，因为 if 和之前一样有空的主体，后面跟着另一个块 blk A ，它不是 if 的主体。现在，当在块后面找到 else if 时，它无法与任何导致此错误的 if 匹配。如果我们用语句代替块，也会发生同样的情况：
if(...) ;
do_something;
else {
...
}
There are ; at the end of if statements.
Cause of error:
if(...) ;
{
...
}
Will not cause any syntax error as the body of if is empty and the following block always gets executed. But
if(...) ;
{
// blk A
} else {
...
}
will cause Unexpected else syntax error because the if as before has empty body and is followed by another block blk A which is not if's body. Now when an else if found after the block it cannot be matched with any if causing this error. The same would happen if we'd statement(s) in place of a block:
$agent = getenv("HTTP_USER_AGENT");
if (preg_match("/MSIE/i", $agent)) {
$result = "You are using Microsoft Internet Explorer";
} else if (preg_match("/Mozilla/i", $agent)) {
$result = "You are using Mozilla firefox";
} else {
$result = "you are using $agent";
}
echo $result;
两件事：
if 子句末尾有一个分号。这意味着后续的左大括号是始终执行的本地块。这导致了一个问题，因为后来您有一个 else 语句没有附加到 if 语句；
执行 "$agent" 是不必要的，也不建议这样做。只需传入 $agent。
Try:
$agent = getenv("HTTP_USER_AGENT");
if (preg_match("/MSIE/i", $agent)) {
$result = "You are using Microsoft Internet Explorer";
} else if (preg_match("/Mozilla/i", $agent)) {
$result = "You are using Mozilla firefox";
} else {
$result = "you are using $agent";
}
echo $result;
Two things:
You had a semi-colon at the end of your if clauses. That means the subsequent opening brace was a local block that is always executed. That caused a problem because later you had an else statement that wasn't attached to an if statement; and
Doing "$agent" is unnecessary and not recommended. Simply pass in $agent.
发布评论
评论（4）
if语句末尾有;。错误原因：
不会导致任何语法错误，因为
if的正文为空，并且以下块< em>总是被执行。但会导致
Unexpected else语法错误，因为if和之前一样有空的主体，后面跟着另一个块blk A，它不是 if 的主体。现在，当在块后面找到elseif 时，它无法与任何导致此错误的if匹配。如果我们用语句代替块，也会发生同样的情况：There are
;at the end ofifstatements.Cause of error:
Will not cause any syntax error as the body of
ifis empty and the following block always gets executed. Butwill cause
Unexpected elsesyntax error because theifas before has empty body and is followed by another blockblk Awhich is not if's body. Now when anelseif found after the block it cannot be matched with anyifcausing this error. The same would happen if we'dstatement(s) in place of a block:尝试：
两件事：
if 子句末尾有一个分号。这意味着后续的左大括号是始终执行的本地块。这导致了一个问题，因为后来您有一个
else语句没有附加到if语句；执行
"$agent"是不必要的，也不建议这样做。只需传入$agent。Try:
Two things:
You had a semi-colon at the end of your if clauses. That means the subsequent opening brace was a local block that is always executed. That caused a problem because later you had an
elsestatement that wasn't attached to anifstatement; andDoing
"$agent"is unnecessary and not recommended. Simply pass in$agent.删除包含“if”的行末尾的分号。
remove the semi-colons from the end of the lines with "if" in them.
为什么这里有分号？
if (preg_match("/MSIE/i", "$agent"));此处else if (preg_match("/Mozilla/i", "$agent"));< /代码>Why do you have a semicolon here?
if (preg_match("/MSIE/i", "$agent"));and hereelse if (preg_match("/Mozilla/i", "$agent"));