PHP语法中的“\”实际意味着什么？

Question

I have a piece of code and i keep getting syntax errors for codes like thess :

$query ="SELECT * from `jos_menu` where `id` = ".'\".$parent.'\";

Now when i reformat it as :

$query ="SELECT * from `jos_menu` where `id` = ".$parent;

That is when i remove : '\" it works fine. So i am just wondering, what does ('\") actually do ???

Answer 1

The only problem with

$query ="SELECT * from `jos_menu` where `id` = ".'\".$parent.'\";

Is that you missed a few ':

$query ="SELECT * from `jos_menu` where `id` = ".'\"'.$parent.'\"';

In PHP, a string can either be:

$var = 'This is a string';

Or

$var = "This is a string";

If you want to put " inside a string that you already started with ", you need tell PHP that you don't want your second " to end the string but use the character " as part of the string itself. This is what \" does. It tells PHP that Don't give the " character any special meaning; since normally if you started the string with ", the next " would end the string.

\ means remove any "special" meaning to the next character

This only works if the character after the \ would have had special meaning. Some examples:

Suppose we want to print Hello "World". I am a string!:

$var = "Hello "World". I am a string!";

In this example we will have errors. Since we started the string with ", the next " will close the string. So what PHP thinks:

1. " Start of string
2. Hello part of string variable.
3. " Hey, since I saw that the string was started with ", this must mean the end of it!
4. World" <-- Error

Stop processing and throw errors.

However, if we write:

$var = "Hello \"World\". I am a string!";

Now, PHP thinks:

1. " Start of string
2. Hello part of string variable
3. \ Ah, okay, the next character I should remove any special meaning
4. " Okay, this is immediately after \, so I just use it normally, as a ".
5. World part of string
6. \ Okay, the next character I will remove any special meaning
7. " This is now a normal "
8. . I am a string! - part of string variable.
9. " Ah! Since the string was started with ", this must be the ending.
10. ; ends statement.

Hopefully this clarifies things for you.