I am trying to insert a string at a position for C# string, its failing
here is the snippet.
if(strCellContent.Contains("<"))
{
int pos = strCellContent.IndexOf("<");
strCellContent.Insert(pos,"<");
}
please tell me the solution
The return value contains the new string that you desire.
strCellContent = strCellContent.Insert(pos,"<");
Gunner and Rhapsody have given correct changes, but it's worth knowing why your original attempt failed. The String type is immutable - once you've got a string, you can't change its contents. All the methods which look like they're changing it actually just return a new value. So for example, if you have:
string x = "foo";
string y = x.Replace("o", "e");
the string x refers to will still contain the characters "foo"... but the string y refers to will contain the characters "fee".
This affects all uses of strings, not just the particular situation you're looking at now (which would definitely be better handled using Replace, or even better still a library call which knows how to do all the escaping you need).
I think you might be better of with a Replace instead of an Insert:
strCellContent = strCellContent.Replace("<", "<");
Maybe doing Server.HtmlEncode() is even better:
strCellContent = Server.HtmlEncode(strCellContent);
When I look at your code I think you want to do a replace, but try this:
if(strCellContent.Contains("<"))
{
int pos = strCellContent.IndexOf("<");
strCellContent = strCellContent.Insert(pos,"<");
}
.Contains is not a good idea here, because you need to know the position. This solution will be more efficient.
int pos = strCellContent.IndexOf("<");
if (pos >= 0) //that means the string Contains("<")
{
strCellContent = strCellContent.Insert(pos,"<"); //string is immutable
}
As others have explained with the code, I will add that
The value of the String object is the
content of the sequential collection,
and that value is immutable (that is,
it is read-only).
For more information about the immutability of strings, see the Immutability and the StringBuilder Class section.
from: http://msdn.microsoft.com/en-us/library/system.string.aspx
Related
I have a string List<string> this would apply to all Lists. I needed to get the first item in a string list and then convert what I got back to a string.
Here is the working code using linq:
public List<string> AppGroup = new List<string>();
var group = SearchParameters.AppGroup.Take(1);
string firstAppGroup = String.Join(",", group.ToArray());
My question would be; Is this the best method to do what I am going for? Is there a better or shorter way to write this out? A good example of considering performance would be appreciated. If what I have is fine and no changes are needed, please let me know.
I am using framework 3.5 and above.
Your current means of grabbing the first item in the list is somewhat long-winded, and stems from the fact that using Take(1) returns an IEnumerable rather than the item in question.
Assuming SearchParameters.AppGroup is List<string>
string firstAppGroup =
SearchParameters.AppGroup.FirstOrDefault(); //returns null on empty set
is a much briefer way of stating the same intent.
EDIT:
As #CodeInChaos states, if you don't want to deal with a null value, use the null-coalescing operator to substitute an empty string in the case that null is returned:
string firstAppGroup =
SearchParameters.AppGroup.FirstOrDefault() ?? string.Empty;
Could be a one liner:
string firstAppGroup = String.Join(",", SearchParameters.AppGroup.First());
I have a function in a class called Function, like below:
public int SearchedRecords(String [] recs)
{
int counter = 0;
String pat = "-----";
String[] records = recs;
foreach (String line in records)
{
if (line.Contains(pat) == true)
{
counter++;
}
}
return counter;
}
And I am calling this method from my main class this way:
String [] file = File.ReadAllLines("C:/Users.../results.txt");
int counter = Function.SearchedRecords( []file);
But I get an error saying:
;expected
What is wrong?
Another question: The function above is counting from a file all the lines with the pattern ----- in them (even if with more dashes, or if the line has some chars before or after the dashes). Am I right?
It's something like the patterns in Java so maybe there is an other way.
Can you enlighten me?
Remove the [] from your parameter.
e.g.
int counter = Function.SearchedRecords(file);
And yes, your assumption about the behavior of the Contains method is correct - you'll match any line containing five consecutive dashes, regardless of what characters are before or after them.
If you want to parse for exactly five dashes, with nothing before or after them I suggest looking into the RegEx class (regular expressions).
Change
int counter = Function.SearchedRecords( []file);
to
int counter = Function.SearchedRecords(file);
and yes, this will work, for that string.
However Contains is case sensitive, if you were matching on a name, or another string with alphabetic characters, the case would have to be identical to match e.g. line.Contains("Binary Worrier") will not match a string "Hello binary worrier".
Also, reading the entire file into memory is fine if you know that the file will always be small, this method gets less efficient the larger the file.
Better to always use something like System.IO.StreamReader or System.IO.File.ReadLines (available in .Net 4 and later), these allow you to consume the file one line at a time. e.g.
using (var reader = new System.IO.StreamReader("MyFile.txt"))
{
while(!reader.EndOfStream)
{
string line = reader.ReadLine();
if (line.Contains(pattern))
counter++;
}
}
Change it to
int counter = Function.SearchedRecords(file);
Remove '[]' from a method call. Yes, your function seems to count what you want.
First of all you need to create an instance of function class and then run the function. Hope following code helps
Function fb = new Function();
int counter = fb.SearchedRecords(file);
Right now, you are using SearchRecords as an static function of a static class which doesn't require instantiation.
You can do this in a shorter way using LINQ:
int counter = file.Count(line => line.Contains("-----"));
I am working on a file parser, and this bit of code is not giving me what I want. Before I go any farther, I should mention that I did not write this program, I am only editing the source to fix this specific problem. Also, I can compile the code, so that is not a problem (you know how downloaded programs always have compile errors). Here's the code.
case EsfValueType.Binary4E: //System.String[]
{
int size = (int)(this.reader.ReadUInt32() - ((uint)this.reader.BaseStream.Position));
var strings = new string[size / 4];
for (int i = 0; i < size / 4; i++)
strings[i] = this.stringValuesUTF16[this.reader.ReadUInt32()];
esfValue.Value = strings.ToString();
break;
}
Now, I added the .ToString(); part to the above line, but it made no difference. The problem is that esfValue.Value ends up with System.String[] as it's value, and I want the value of the System.String object. If you can make sense out of this and tell me what is wrong, it would be appreciated.
The program name is ESF Editor 1.4.8.0.
case EsfValueType.Binary4E: //System.String[]
{
int size = (int)(this.reader.ReadUInt32() - ((uint)this.reader.BaseStream.Position));
var strings = new StringBuilder();
for (int i = 0; i < size / 4; i++)
{
strings.Append(this.stringValuesUTF16[this.reader.ReadUInt32()]); //or AppendLine, depending on what you need
}
esfValue.Value = strings.ToString();
break;
}
The strings variable is an array of strings - the Array class does not override the default ToString() implementation which returns the type of the object.
You need to concatenate all the strings in the array - either looping and concatenating or using LINQ and assign the resulting string to esfValue.Value. Of course, this assumes you want the values all in one string, one after the other.
Your issue is that strings isn't a single string, its an array of strings. As a result your call to ToString is calling Object.ToString(), which returns the type of the object.
Maybe you want something like
esfValue.Value = strings.Aggregate((acc, next) => acc + next)
which will simply concatenate all the strings together.
When you do a .ToString() on a class that doesn't override the .ToString() base method to return a custom string (which string[] doesn't), you're always going to get the type's namespace/class as the result.
Arrays, in and of themselves, don't have values. What value are you trying to get? Are you trying to join the array into a single, character-delimited string? If so, this would work:
esfValue.Value = string.Join(",", strings);
Just replace the , with whatever character you want to delimit the array with.
I think you just need to join the string values contained in the string array. In order to do so, you need to call String.Join and pass the string separator and the string array. It returns a single System.String.
I'm trying to maniplulate a string without making a big issue out of it and spreading it out onto multiple lines, so I'm using some chaining to achieve this. The question I have is, how do I use string.Substring() to drop the last character off my string in this context?
In PHP I can pass a negative number as an argument (i.e. substr(-1)) to achieve this, but obviously this isn't how C# works.
mystring = mystring.Replace('_', ' ').Substring(???);
Also, what is the actual name for the technique used above? I always referred to it as a callback chain, but a callback chain I now think is something completely different.
Please note I want to avoid:
mystring = mystring.Replace('_', ' ');
mystring = mystring.Substring(0, mystring.Length - 1);
Thanks in advance for your time and kind consideration.
Iain
Thanks for your answers guys. It's funny that people can have such strong opinions about string manipulation and other "competing" languages :)
You could write an Extension method RightStrip(). You can't overload SubString for negative start positions.
static string RightStrip(this string s, int n)
{
return s.Substring(0, s.Length - n);
}
string s = "Hello World!";
s = s.Replace('e', 'a').RightStrip(1);
Create an extension class like this:
public static class MyStringExtensions
{
public static string RemoveCharactersFromEnd(this string s, int n)
{
string result = string.Empty;
if (string.IsNullOrEmpty(s) == false && n > 0)
{
result = s.Remove(s.Length - n, n);
}
return result;
}
}
Call it:
Console.WriteLine("test!!".RemoveCharactersFromEnd(2));
In your sample, you are chaining to a method that doesn't change the length of the original string. Hence answers suggesting using SubString with (originalLength-1), which of course doesn't work in the general case.
The answer as you seem to have realized is - you can't do it in the general case, where previous methods in the chain have modified the length.
But you can write your own extension method in 3.5 to do what you want. Something like the following or a variant thereof:
public static string PhpSubstring(this string value, int length)
{
if (length < 0) length = value.Length - length;
return String.Substring(value, length);
}
Besides everyone else mentioning the term method chaining, or what some call a fluent interface, I had a note or two I wanted to add.
What I wanted to suggest is that the cool thing about extension methods is that you can easily define your own type of transformation functions that feel the same as this, including system methods such as Replace and ToLower, etc.... something that takes some input and returns some kind of transformed string.
The particular transformation you are asking for (cut off the right-most char) might seem clunky if you have to use Substring directly, but you can hide this away neatly in something like:
public string CutOff(this string s, int c)
{
return s.Substring(0, s.Length - c);
}
...
return myVal.CutOff(1);
(or at least, i think this should work!)
Best of luck!
Method chaining is the term you're looking for. It's true that you cannot pass a negative character like that, but you can still chain the methods:
mystring = mystring.Replace('_', ' ').Substring(0, mystring.Length - 1);
since the string replace in this case, does not affect the length of the string
mystring = mystring.Replace('_', ' ').Remove(mystring.length -1)
However I would consider this a bad idea since the assignment of mystring doesn't happen until after all the manipulation and change in the length of the string in previous calls will result in unexpected behavior.
To further Konamiman's comment:
Just because PHP allows bizarre (and frankly dirty and dangerous) overloads and parameters such as negative starts and counts in SubString, it doesn't mean it's the right, correct or proper way of doing it.
Substring(0, mystring.Length - 1) is the de facto way of trimming off the last character of a string in a wide variety of languages.
You could always use regex:
mystring = new Regex("^(.*).$").Match(mystring.Replace('_', ' ')).Groups[1].Value;
Also, since you're just going to remove that last character, it does not matter if it was a '_' that got replaced by a ' '. This would work just fine:
mystring = mystring.Substring(0, mystring.Length - 1).Replace('_', ' ');
I've found what seems to be the C# equivalent of a FOR-CASE structure in a project I'm working on:
foreach (string param in params.Split(';'))
{
string[] parts = param.Split('=');
string key = parts[0].Trim().ToLower();
string value = parts[1].Trim();
switch (key)
{
case "param1": this.param1 = value; break;
case "param2": this.param2 = value; break;
case "param3": this.param3 = value; break;
case "param4": this.param4 = value; break;
default: break;
}
}
(Variable names changed to protect the guilty.)
How would you implement this code?
I don't think the code in your question is anything like the code you linked to....
The code in the question looks like something I might do if I wrote a command line tool.
Am I stupid for not seeing whats wrong with the code in the question?
An alternative is to use reflection to fill parameter value variables. I've done it that ways sometimes too.
BTW: I once wrote a program in a script language that had switch as the only flow control mechanism and no gosub/return. The code in my program was structured a bit like the one you linked to. A massive switch on a sort of instruction pointer variable that got reassigned at the end of every case and an almost infinite loop around the switch. It got the job done.
I see you that you already have multiple fields in your class that you use to hold the variables. In that case, what you are doing is fine.
Otherwise, you can have 1 HashTable (maybe add in the C# indexor as a twist) to hold all of them, and your loop will end up like this:
foreach (string param in params.Split(';'))
{
string[] parts = param.Split('=');
string key = parts[0].Trim().ToLower();
string value = parts[1].Trim();
MyHashTable[key] = value;
}
The problem with this approach is that you should only have 1 type of value. For example, if your param list can contain both string and int types, it makes the code messier, especially you need to perform error checking and validation and stuff.
I personally would stick with what you already have.
You could use reflection for this:
Type t = this.GetType();
foreach (string param in params.Split(';'))
{
string[] parts = param.Split('=');
string key = parts[0].Trim().ToLower();
string value = parts[1].Trim();
t.GetProperty(key).SetValue(this, value, null);
}
For what it's worth, the WTF article was a WTF because its outer loop was completely useless, as noted in the article - it was just as easy, and more direct, just to set an index variable directly than to loop and test it.
Not sure if I understand either but it sounds like you're complicating yourself. Don't reinvent the wheel, use BCL classes as much as you can, these classes are proven to work efficiently and save you lots of time. Sounds like you could implement it with some sort of Dictionary<,> along with, like Guge suggested, Reflection.
I actually think the OP's code is fine. It's not perfect -- there might be simpler or cleaner ways to do it, but it effectively allows for readable mappings between member/property names and input-parameter names. It leaves your properties strongly typed (unlike the hashmap/dictionary solutions, unless your class has only one type for all its properties...) and gives you one fairly-obvious place to fix or add mappings.
Or Regex:
string parms = "param1=1;param2=2;param3=3";
string[] parmArr = parms.Split(';');
string parm1 = Regex.Replace(parmArr[0], "param1=", "");
string parm2 = Regex.Replace(parmArr[1], "param2=", "");
string parm3 = Regex.Replace(parmArr[2], "param3=", "");