C# String.Format 指定字符串宽度和对齐方式

String.Format("{0,-10}",str);//这个表示第一个参数str字符串的宽度为10，左对齐

String.Format("{0,10}",str);//这个表示第一个参数str字符串的宽度为10，右对齐

参考：From MSDN

Format Item Syntax

Each format item takes the following form and consists of the following
components:

{index[,alignment][:formatString]}

The matching braces ("{" and "}") are required.

Index Component

The mandatory index component, also called a parameter specifier, is a
number starting from 0 that identifies a corresponding item in the list of
objects. That is, the format item whose parameter specifier is 0 formats the
first object in the list, the format item whose parameter specifier is 1 formats
the second object in the list, and so on.

Multiple format items can refer to the same element in the list of objects by
specifying the same parameter specifier. For example, you can format the same
numeric value in hexadecimal, scientific, and number format by specifying a
composite format string like this: "{0:X} {0:E} {0:N}".

Each format item can refer to any object in the list. For example, if there
are three objects, you can format the second, first, and third object by
specifying a composite format string like this: "{1} {0} {2}". An object that is
not referenced by a format item is ignored. A runtime exception results if a
parameter specifier designates an item outside the bounds of the list of
objects.

Alignment Component

The optional alignment component is a signed integer indicating the
preferred formatted field width. If the value of alignment is less than
the length of the formatted string, alignment is ignored and the length
of the formatted string is used as the field width. The formatted data in the
field is right-aligned if alignment is positive and left-aligned if
alignment is negative. If padding is necessary, white space is used. The
comma is required if alignment is specified.

Format String Component

The optional formatString component is a format string that is
appropriate for the type of object being formatted. Specify a if the corresponding object is a numeric value, a
if the corresponding object is a object, or an
if the corrersponding object is an enumeration value. If
formatString is not specified, the general ("G") format specifier for a
numeric, date and time, or enumeration type is used. The colon is required if
formatString is specified.