php string comparison unexpected type juggling
I encountered a strange and unexpected behavior in PHP while comparing some string values. The first two statements below return true when I would expect them to return false. The last statement returns false as expected. I'm aware of PHP's Type Juggling, but what I understand from the docs is that type juggling happens when you are comparing two different data types like a string and an integer. In the examples below though both literals are strings. Does this mean that when you are doing string comparison in PHP it inspects both strings to see if they look like integers and if so type casts the both of them to integers and then compares those integer values. So my question is under what conditions does this behavior happen, how exactly does string comparison work in PHP?
var_dump("10" == "10.0000");
var_dump("10" == "+10.");
var_dump("10" == "10 ");
#output
bool(true)
bool(true)
bool(false)
Updates
So baba's answer below comparison involves numerical strings really helped in getting me to understand what's going on. The function is_numeric will return to you whether or not a string is considered to be a numeric string. interestingly "10 " is not considered a numeric string but " 10" is. I dug around the PHP source code and I believe the implementation of is_numeric is in the is_numeric_string_ex function. From that one can tell exactly when PHP will treat a string as a numeric string.
You are getting error because of the position of the space this would return true
var_dump("10" == " 10"); // true
So if you RUN
var_dump("10" == "10 "); //false
What you are actually Running is because it would be treated as a string
var_dump("10" == 0); //false
This is because Type juggling would convert "10 " to 0 this is in the PHP Documentation
FROM PHP DOC
TRUE if $a is equal to $b after type juggling.
If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically. These rules also apply to the switch statement. The type conversion does not take place when the comparison is === or !== as this involves comparing the type as well as the value.
If you want to trick type juggling
var_dump("10" == 0 + "10 "); // true
This is Because
An example of PHP's automatic type conversion is the addition operator '+'. If either operand is a float, then both operands are evaluated as floats, and the result will be a float. Otherwise, the operands will be interpreted as integers, and the result will also be an integer. Note that this does not change the types of the operands themselves; the only change is in how the operands are evaluated and what the type of the expression itself is.
我猜想肯定的答案是埋在PHP-src / Zend / zend_operators.c中的compare_function的巨大地方，以及在那里使用的宏。
In this case, all the 'strings' except the last one, are treated like floats or integers, and then compared. Thats why line 1 and 2 give a true.
In line 3 there is a space in the string, and that means for php that is is a 'real' string, and that line gets strings compared.
I do not like loose typed languages either, but for php this is the way it works.
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