Formatting Strings

Maharishi Bhatia

Hi all Can anyone suggest me which way of string replacment is much better ?? 1) string str = "Date today is " + Date.Now.ToString() + " !!!!" Or 2) string str = String.Format("Date today is {0} !!!!",Date.Now.ToString()) Thanxs Maharishi Bhatia

Heath Stewart

Never concatenate strings using + - it's very expensive since two iterations for each string and each concatenation are necessary, making it an (m-1)O(2n) operation where n is the number of character for two strings and m is the number of strings. Use String.Concat or String.Format like you're doing, but don't use ToString. What do you thing String.Format is for? Lets say you wanted to format the date using the long date format. Just use the following:

string s = string.Format("The date is {0:D}.", DateTime.Now);

If you use ToString, you loose that ability (unless you use the overload for DateTime.ToString which takes a string and optionally a different culture's IFormatProvider. I'll be submitting an article on this topic in the next couple days. You might want to keep a look out and read it.

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Spanky3

bloody hell never knew it was expensive to use ToString() ! Well you learn something everyday

Heath Stewart

It isn't expensive to use ToString (unless the implementation is crappy), I said it was expensive to concat strings using +. Using ToString in the variable argument list for String.Format (and the like) is not only unnecessary but in many cases dumb since you loose the ability to apply custom formats (unless you pass the format specifiers as args to the ToString overload for the IFormattable implementation).

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Judah Gabriel Himango

Heath Stewart wrote: Never concatenate strings using + ...Use String.Concat C# code that 'pluses' strings together gets IL compiled down to .Concat, right? Maybe I'm misunderstanding you. --------------------------- He who knows that enough is enough will always have enough. -Lao Tsu

Heath Stewart

For the Microsoft C# compiler, yes, and under certain circumstances - which typically warrant String.Format for better control. Depending on the operands you're passing, the compiler doesn't always optimize using String.Concat either.

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Alvaro Mendez

Well then, if you take into account that it's almost always optimized into String.Concat, then wouldn't you say that using + is actually much quicker than using String.Format, which involves parsing and appending? From a readibility stand point, the + operator is superior in my opinion. Now, if special formatting is necessary, then the Format method is available -- for formatting purposes. Regards, Alvaro

Give a man a fish, he owes you one fish. Teach a man to fish, you give up your monopoly on fisheries.

Alvaro Mendez

string str = "Date today is " + Date.Now + " !!!!"; ToString() is automatically called for you. :-) Regards, Alvaro

Give a man a fish, he owes you one fish. Teach a man to fish, you give up your monopoly on fisheries.

Heath Stewart

It depends on the circumstances, I'd say. Like you said, for special formatting using String.Format is definitely better, though you could accomplish this task with + or String.Concat if you use the overloaded ToString that corresponds to the IFormattable implementation.

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