Can I use String.Format() to pad a certain string with arbitrary characters?
Console.WriteLine("->{0,18}<-", "hello");
Console.WriteLine("->{0,-18}<-", "hello");
returns
-> hello<-
->hello <-
I now want the spaces to be an arbitrary character. The reason I cannot do it with padLeft or padRight is because I want to be able to construct the format string at a different place/time then the formatting is actually executed.
--EDIT--
Seen that there doesn't seem to be an existing solution to my problem I came up with this (after Think Before Coding's suggestion)
--EDIT2--
I needed some more complex scenarios so I went for Think Before Coding's second suggestion
[TestMethod]
public void PaddedStringShouldPadLeft() {
string result = string.Format(new PaddedStringFormatInfo(), "->{0:20:x} {1}<-", "Hello", "World");
string expected = "->xxxxxxxxxxxxxxxHello World<-";
Assert.AreEqual(result, expected);
}
[TestMethod]
public void PaddedStringShouldPadRight()
{
string result = string.Format(new PaddedStringFormatInfo(), "->{0} {1:-20:x}<-", "Hello", "World");
string expected = "->Hello Worldxxxxxxxxxxxxxxx<-";
Assert.AreEqual(result, expected);
}
[TestMethod]
public void ShouldPadLeftThenRight()
{
string result = string.Format(new PaddedStringFormatInfo(), "->{0:10:L} {1:-10:R}<-", "Hello", "World");
string expected = "->LLLLLHello WorldRRRRR<-";
Assert.AreEqual(result, expected);
}
[TestMethod]
public void ShouldFormatRegular()
{
string result = string.Format(new PaddedStringFormatInfo(), "->{0} {1:-10}<-", "Hello", "World");
string expected = string.Format("->{0} {1,-10}<-", "Hello", "World");
Assert.AreEqual(expected, result);
}
Because the code was a bit too much to put in a post, I moved it to github as a gist:
http://gist.github.com/533905#file_padded_string_format_info
There people can easily branch it and whatever :)
This question is related to
c#
formatting
padding
string.format
There is another solution.
Implement IFormatProvider to return a ICustomFormatter that will be passed to string.Format :
public class StringPadder : ICustomFormatter
{
public string Format(string format, object arg,
IFormatProvider formatProvider)
{
// do padding for string arguments
// use default for others
}
}
public class StringPadderFormatProvider : IFormatProvider
{
public object GetFormat(Type formatType)
{
if (formatType == typeof(ICustomFormatter))
return new StringPadder();
return null;
}
public static readonly IFormatProvider Default =
new StringPadderFormatProvider();
}
Then you can use it like this :
string.Format(StringPadderFormatProvider.Default, "->{0:x20}<-", "Hello");
Simple:
dim input as string = "SPQR"
dim format as string =""
dim result as string = ""
'pad left:
format = "{0,-8}"
result = String.Format(format,input)
'result = "SPQR "
'pad right
format = "{0,8}"
result = String.Format(format,input)
'result = " SPQR"
You could encapsulate the string in a struct that implements IFormattable
public struct PaddedString : IFormattable
{
private string value;
public PaddedString(string value) { this.value = value; }
public string ToString(string format, IFormatProvider formatProvider)
{
//... use the format to pad value
}
public static explicit operator PaddedString(string value)
{
return new PaddedString(value);
}
}
Then use this like that :
string.Format("->{0:x20}<-", (PaddedString)"Hello");
result:
"->xxxxxxxxxxxxxxxHello<-"
Edit: I misunderstood your question, I thought you were asking how to pad with spaces.
What you are asking is not possible using the string.Format alignment component; string.Format always pads with whitespace. See the Alignment Component section of MSDN: Composite Formatting.
According to Reflector, this is the code that runs inside StringBuilder.AppendFormat(IFormatProvider, string, object[]) which is called by string.Format:
int repeatCount = num6 - str2.Length;
if (!flag && (repeatCount > 0))
{
this.Append(' ', repeatCount);
}
this.Append(str2);
if (flag && (repeatCount > 0))
{
this.Append(' ', repeatCount);
}
As you can see, blanks are hard coded to be filled with whitespace.
Source: Stackoverflow.com