string.format functionality

Hello friends,

Following are some very good explanation of string.format functionality. Please go through it will really help.

"I see stuff like {0,-8:G2} passed in as a format string. What exactly does that do?" -- Very Confused String Formatter

The above format can be translated into this:

"{[,][:]}"

argument index: This represent which argument goes into the string.

String.Format("first = {0};second = {1}", "apple", "orange");

String.Format("first = {1};second = {0}", "apple", "orange");

gives the following strings:

"first = apple;second = orange"

"first = orange;second = apple"

alignment (optional): This represent the minimal length of the string.

Postive values, the string argument will be right justified and if the string is not long enough, the string will be padded with spaces on the left.

Negative values, the string argument will be left justied and if the string is not long enough, the string will be padded with spaces on the right.

If this value was not specified, we will default to the length of the string argument.

String.Format("{0,-10}", "apple"); //"apple "

String.Format("{0,10}", "apple"); //" apple"

format string (optional): This represent the format code.

Numeric format specifier is available here. (e.g. C, G...etc.)
Datetime format specifier is available here.

Enumeration format specifier is available here.

Custom Numeric format specifier is available here. (e.g. 0. #...etc.)

Custom formatting is kinda hard to understand. The best way I know how to explain something is via code:

int pos = 10;

int neg = -10;

int bigpos = 123456;

int bigneg = -123456;

int zero = 0;

string strInt = "120ab";

String.Format("{0:00000}", pos); //"00010"

String.Format("{0:00000}", neg); //"-00010"

String.Format("{0:00000}", bigpos); //"123456"

String.Format("{0:00000}", bigneg); //"-123456"

String.Format("{0:00000}", zero); //"00000"

String.Format("{0:00000}", strInt); //"120ab"

String.Format("{0:#####}", pos); //"10"

String.Format("{0:#####}", neg); //"-10"

String.Format("{0:#####}", bigpos); //"123456"

String.Format("{0:#####}", bigneg); //"-123456"

String.Format("{0:#####}", zero); //""

String.Format("{0:#####}", strInt); //"120ab"

While playing around with this, I made an interesting observation:

String.Format("{0:X00000}", pos); //"A"

String.Format("{0:X00000}", neg); //"FFFFFFF6"

String.Format("{0:X#####}", pos); //"X10"

String.Format("{0:X#####}", neg); //"-X10"

The "0" specifier works well with other numeric specifier, but the "#" doesn't. Umm... I think the "Custom Numeric Format String" probably deserve a whole post of it's own. Since this is only the "101" post, I'll move on to the next argument in the format string.

zeros (optional): It actually has a different meaning depending on which numeric specifier you use.

int neg = -10;

int pos = 10;

// C or c (Currency): It represent how many decimal place of zeros to show.

String.Format("{0:C4}", pos); //"$10.0000"

String.Format("{0:C4}", neg); //"($10.0000)"

// D or d (Decimal): It represent leading zeros

String.Format("{0:D4}", pos); //"0010"

String.Format("{0:D4}", neg); //"-0010"

// E or e (Exponential): It represent how many decimal places of zeros to show.

String.Format("{0:E4}", pos); //"1.0000E+001"

String.Format("{0:E4}", neg); //"-1.0000E+001"

// F or f (Fixed-point): It represent how many decimal places of zeros to show.

String.Format("{0:F4}", pos); //"10.0000"

String.Format("{0:F4}", neg); //"-10.0000"

// G or g (General): This does nothing

String.Format("{0:G4}", pos); //"10"

String.Format("{0:G4}", neg); //"-10"

// N or n (Number): It represent how many decimal places of zeros to show.

String.Format("{0:N4}", pos); //"10.0000"

String.Format("{0:N4}", neg); //"-10.0000"

// P or p (Percent): It represent how many decimal places of zeros to show.

String.Format("{0:P4}", pos); //"1,000.0000%"

String.Format("{0:P4}", neg); //"-1,000.0000%"

// R or r (Round-Trip): This is invalid, FormatException is thrown.

String.Format("{0:R4}", pos); //FormatException thrown

String.Format("{0:R4}", neg); //FormatException thrown

// X or x (Hex): It represent leading zeros

String.Format("{0:X4}", pos); //"000A"

String.Format("{0:X4}", neg); //"FFFFFFF6"

// nothing: This is invalid, no exception is thrown.

String.Format("{0:4}", pos)); //"4"

String.Format("{0:4}", neg)); //"-4"

In summary, there are four types of behaviour when using this specifier:

Leading Zeros: D, X

Trailing Zeros: C, E, F, N, P

Nothing: G

Invalid: R,

Now, that we've gone through the valid specifiers, you can actually use this in more than just String.Format(). For example, when using this withByte.ToString():

Byte b = 10;

b.ToString("D4"); //"0010"

b.ToString("X4"); //"000A"

Reference : http://blogs.msdn.com/kathykam/archive/2006/03/29/564426.aspx