c# string performance - what is faster to compare, string text or string length

Question

hey guys i have to read a huge xml file which consists of over 3 million records and over 10 million nested elements

naturally i am using xmltextreader and have got my parsing time down to about 40 seconds from earlier 90 seconds using multiple optimization tricks and tips

but i want to further save processing time as much as i can hence below question

quite a few elements are of type xs:boolean and the data provider always represents values as "true" or "false" - never "1" or "0"

for such cases my earliest code was:

if (xmlTextReader.Value == "true")
{
    bool subtitled = true;
}

which i further optimized to:

if (string.Equals(xmlTextReader.Value, "true", StringComparison.OrdinalIgnoreCase))
{
    bool subtitled = true;
}

i wanted to know if below would be fastest (because its either "true" or "false")?

if (xtr.value.length == 4)
{
    bool subtitled = true;
}

Answer 1

Yes, it's faster, because you only compare exactly one value, namely the length of the string.

By comparing two strings with each other, you compare each and every character, as long as both characters are the same. So if you're finding a match for the string "true", you're going to do 4 comparisons before the predicate evaluates to true.

The only problem you have with this solution is, that if someday the value is going to change from true to let's say 1, you're going to run into a problem here.

Answer 2

Comparing length will be faster, but less readable. I wouldn't use it unless I profile the performance of the code and conclude that I need this optimization.

Answer 3

Cant you just write a unit test? Run each scenario for example 1000 times and compare the datetimes.

Answer 4

Measuring the length would almost invariably be faster. That said, unless this is an experiment in micro-optimization, I'd just focus on making the code to be readable and convey the proper semantics.

You might also try something like that uses the following approach:

Boolean.TryParse(xmlTextReader.Value, out subtitled)

I know that has nothing to do with your question, but I figured I'd throw it out there anyway.

Answer 5

What about comparing the first character to "t"?

Should (maybe :) be faster than comparing the whole string..

Answer 6

String comparing and parsing is very slow in .Net, I'd recommend avoid intensive using string parsing/comparing in .Net.

If you're forced to do it -- use highly optimized unmanaged or unsafe code and use parallelism.

IMHO.

Answer 7

If you know it's either "true" or "false", the last snippet must be fastest.

Anyway, you can also write:

bool subtitled = (xtr.Value.length == 4);

That should be even faster.