Pad left or right with string format not padleft or padright with arbitrary string

Question

Can I use String Format   to pad a certain string with arbitrary characters   Console WriteLine  - gt  0 18  lt -    hello    Console WriteLine  - gt  0 -18  lt -    hello     returns   - gt              hello lt - - gt hello              lt -   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     - gt  0 20 x   1  lt -    Hello    World        string expected    - gt xxxxxxxxxxxxxxxHello World lt -       Assert AreEqual result  expected      TestMethod  public void PaddedStringShouldPadRight         string result   string Format new PaddedStringFormatInfo     - gt  0   1 -20 x  lt -    Hello    World        string expected    - gt Hello Worldxxxxxxxxxxxxxxx lt -       Assert AreEqual result  expected      TestMethod  public void ShouldPadLeftThenRight         string result   string Format new PaddedStringFormatInfo     - gt  0 10 L   1 -10 R  lt -    Hello    World        string expected    - gt LLLLLHello WorldRRRRR lt -       Assert AreEqual result  expected      TestMethod  public void ShouldFormatRegular         string result   string Format new PaddedStringFormatInfo     - gt  0   1 -10  lt -    Hello    World        string expected   string Format  - gt  0   1 -10  lt -    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

User · Answer

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<-"

User · Answer

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  amp  amp   repeatCount  gt  0         this Append      repeatCount     this Append str2   if  flag  amp  amp   repeatCount  gt  0         this Append      repeatCount       As you can see  blanks are hard coded to be filled with whitespace

User · Answer

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   - gt  0 x20  lt -    Hello

User · Answer

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

[c#] Pad left or right with string.format (not padleft or padright) with arbitrary string

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