Understanding String Formatting

Padding & Alignment

Composite formatting syntax supports three semantic for

• the padding length of each interpolation
• the direction of each padding for interpolation
• the format of each interpolation

What's padding? It fills out a string to a specified length using spaces. If the specified length is less than the length of the string, string remains the same. You can specify the direction to be left or right.

// pad spaces on left
"123".PadLeft(20);
//                 123

The second syntax in composite formatting is a optional integer for the interpolation:

• specify direction of padding by -(pad spaces on left) and pad on right by default
• length of padding

string.Format("{0,20}", 123);
//                 123
string.Format("{0,-20}", 123);
// 123                ^ ends here

Format Convention

Numeric Format

• G for General
• C for Currency with decimal precision supported
• B for Binary numeric
• D for padding integers to specified trailing digit count
• E for Exponential format
  • e for lowercase, 1.23e+02 for example.
• F for Fixed-point numeric
• N for Numeric
  • formats to ddd,ddd.ddd..., trailing precision specifier is allowed
• P for Percentage
• X for heXadecimal
  • x for lowercase hexadecimal
  • trailing number after X or x left pads to length with 0
• R for Round-trip
  • supported for Double, Single, Half and BigInteger only.
  • ensures the converted string represents the exact precision of the number.

ToString & IFormattable