How to delete characters of a string?

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Hello, i want know how can i delete characters of an string, for example, delete the characters 0 and 4 of this string.

string frase  = "Ayer estaba solo";

Best regards
Ángel Manuel

Posted 2-Feb-11 19:29pm

Ángel Manuel García Carmona

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5 solutions

Solution 1

To delete 0 try something like this -

while(frase.indexof(0)!=-1)
{
frase.Remove(frase.indexOf(0));
}

You can paramterize this method to pass all values.

Posted 2-Feb-11 19:32pm

Abhinav S

Comments

Sergey Alexandrovich Kryukov 3-Feb-11 1:40am

Sorry Abhinav, this will not work. String is immutable. When you call string method, you return another string but discard the return. Test it -- in won't work.
Also, this is very ineffective. Please fix.
--SA

Abhinav S 3-Feb-11 1:45am

The OP has changed the tag from C# to C++. So this answer does not hold good anyway.

Sergey Alexandrovich Kryukov 3-Feb-11 1:50am

Abhinav, are you sure? I also saw C#, but where is the past revision of the Question? Is is possible?
--SA

Sergey Alexandrovich Kryukov 3-Feb-11 1:44am

My answer is using StringBuilder which is designed for string manipulations and optimized for speed. Please see.
--SA

Sergey Alexandrovich Kryukov 3-Feb-11 1:46am

Thank you.
--SA

Solution 2

Here is how:

C#

string frase  = "Ayer estaba solo";
System.Text.StringBuilder sb = new System.Text.StringBuilder(frase);
sb.Remove(1, 4);
frase = sb.ToString();

It's important to use StringBuilder for speed, even simple concatenations are faster then with string. The method string.Format is also faster then string equivalent concatenations.

Attention! OP changed a tag from C# to C++. I cannot be hold responsible for that. My answer was in C# when the tag was C#. Please do not down-vote based on that.

—SA

Posted 2-Feb-11 19:43pm

Sergey Alexandrovich Kryukov

Updated 2-Feb-11 19:48pm

v3

Solution 5

I would try a method similar to this.
Note: i just wrote this method on the fly to give the OP another idea.

C#

string remove_char_range(string const& str, unsigned const& start, unsigned const& end)
{
string newStr = "";
unsigned  i = 0;
for_each(str.cbegin(),str.cend(),[&i,&newStr, &start, &end](char const& ch)
{
//if i is in the range provided do not doing anything. else add to the new string
if (i >= start && i <= end)
{
}
else
newStr += ch;
//increment i
i++;
});
return newStr;
}

I just thought I would give it a try. if anyone has a comment i would like to hear it. I am just a student and I am sure there is a better way to do this.
robNO.

Posted 3-Feb-11 12:22pm

RobNO

Comments

Niklas L 4-Feb-11 4:10am

This is rather inefficient. The function also has an awkward signature for mimicking stl. What is wrong with string.erase()? It does what you try in a much more efficient manner. I don't see the point in giving the OP another idea, when there already is an answer both more efficient and robust. Since you're a student, read up on string.capacity().

RobNO 4-Feb-11 18:24pm

Thanks for your reply!!! How can I make this method more efficient? What is awkward about the way i wrote the signature, It is very descriptive is it not(maybe to descriptive)? Nothing is wrong with string.erase(), however being a student I like to try and create my own methods in order to improve. You don't see the point in giving the original poster an idea to perhaps try to create there own methods? How dose reading about a method that returns the memory capacity of a string help me with making an efficient method or are you implying its good general knowledge? Regardless, I posted this method hoping someone would show me a more efficient method, Can you do so? Regards, robNO.

Niklas L 5-Feb-11 5:11am

I will try to make this as short as possible. The main efficiency problem in your implementation is the hidden reallocation of memory in string.operator+=(). It will reallocate memory multiple times, and the longer the string, the more it will have to reallocate. To avoid this, you should use string.reserve() with (str.lenght() - end-start) as an argument before trying to add any characters. I thought string.capacity() would have given you a hint there. Of course the most efficient method would be to do it all in-place. Using any of these two methods will yield a faster function. So, yes, I can write a more efficient method, but no, I won't, because we have string.erase(). About the function signature, if you need indexes, you should use the proper string::size_type, and not unsigned, to avoid portability issues. Could you elaborate on why those indexes are accepted by (const) reference and not by value?

"You don't see the point in giving the original poster an idea to perhaps try to create there own methods?" Reinventing the wheel isn't my deal. Why encourage someone to write something that is already there (and a lot less efficient)? One strength of a programmer is not if he knows how t write a function, but if he knows if he has to. I do this every now and then, and it's really annoying when you find out it has already been done, knowing that you spent extra time on it and maybe even introduced hard to find bugs or performance bottlenecks.

RobNO 5-Feb-11 11:25am

Thanks for your reply!!!

I am aware that reserving memory is faster because the memory does not need to continuously re-allocate memory, however, considering that I wrote that method in less than 2 minutes and never put any though into efficiency, I would have to say its alright. You are also right that I should have used the string classes typedef for string size, I should have put a little more thought into it, but as previously stated I just threw a random idea out. "Could you elaborate on why those indexes are accepted by "(const) reference and not by value?" Yes, their value does not change and I did not want to reallocate the memory for them in the method.

"Why encourage someone to write something that is already there (and a lot less efficient)? " Well, In a way this can be considered Philosophical, however, I do not want to write about anything unrelated to coding. So with that in mind. As a student I believe rewriting code that is already available helps coders learn to improve by coding more, learning there flaws and most importantly becoming creative.

"One strength of a programmer is not if he knows how t write a function, but if he knows if he has to." True!! It already written why waste the time re-writing it, however, another strength for someone learning a language is to learn to rewrite the code by memory,nearly as efficient as the professional who wrote the library; only if they have extra time. Doing that I believe would help with any future projects.

Furthermore, I do not always do this, however, If i have free time I will.

Thanks for your time,
robNO.

Niklas L 5-Feb-11 19:12pm

"I did not want to reallocate the memory for them in the method." You do realize that allocating space for a parameter or local variable comes free of charge, and instead of pushing a simple value onto the stack, you are pushing a reference (an address)? So question remains: What's the gain?

RobNO 5-Feb-11 21:51pm

Thanks for the reply!!!

Whats the loss? My understanding of using a reference was passing the method the address of the variable, rather than passing it by value which would create another variable specifically for that method. Thus, the gain is no creating another variable. I was not aware that creating another variable was free of charge. This is the best answer I can give. Keep in mind I am a student one year into college program, and we have never went into anymore depth than that, therefore that is all the information i can provide. Now i hope you will provide me with a more low level answer.

Thanks for your time,
robNO.

Niklas L 6-Feb-11 7:16am

Creating space on the stack for a parameter or local variable is just a matter of offsetting the stack pointer, which is still done whether you have parameters or not. The compiler will calculate this offset for you, summing up size of local variables, parameters, return values and some extra for house keeping. Do not confuse this with initializing the variables, which does have a cost. Even if you use a reference you will need to keep it in a function local variable, which means you're not really saving any storage in this case. On a 32-bit architecture where the size type is 32 bits, it stands between passing 32 bits as the value of the index, or passing a 32-bit address pointing to it. Both versions will have to store 32 bits in the local stack frame, but the second version is adding an extra level of indirection, which an optimizing compiler probably will turn into the first version anyway. I'm not saying it's wrong to use a reference, just awkward, and maybe an indication that a professional programmer should be targeted for a code review.

Sorry, I did not mean to turn this into a long discussion.
/Niklas

Solution 4

You can use following user define function for deleting specific charactor from string.

Function Call :

char *pStr;
pStr = RemoveChar("Ayer estaba solo",0)  // To remove 0th character
pStr = RemoveChar("Ayer estaba solo",4)  // To remove 4th character

Function Defination:

char* RemoveChar(char str[], int nChPos)
{
  char *pString = str;
  char *pTmpStr;
  int index =0;

  for(int i=0; i<nChPos; i++,index++)
    *(pTmpStr+index) = *(pString+index);

 index++;
 while (*(pString+index) !='\0')
 {
   *(pTmpStr+index-1) = *(pString+index);
   index++;
 }
 *(pTmpStr+index-1) = '\0;
  return pTmpStr;
}

Posted 2-Feb-11 22:58pm

LaxmikantYadav

Updated 3-Feb-11 21:44pm

v5

Comments

Niklas L 3-Feb-11 9:15am

Are you serious? This function contains more issues than it has code lines.
* 20 elements in result array? Come on.
* Never returning any result.
* Algorithm is all wrong.
* Unnecessary function calls.

Niklas L 4-Feb-11 4:20am

Two comments on Revision 5 if you're interested. pTmpStr does most certainly not point to writable memory, and the i variable is unnecessary since index has the same value.

LaxmikantYadav 4-Feb-11 4:54am

Niklas thx for ur valuable comments.

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ShilpiP · Accepted Answer · 2011-02-02T21:50:00

Use erase function : Removes an element or a range of elements in a string from a specified position.

string frase = "Ayer estaba solo";
frase.erase(0,1);
First param is
_Pos: The index of the first character in the string to be removed.
_Count: The number of elements that will be removed if there are as many in the range of the string beginning with _Pos.

How to delete characters of a string?

5 solutions

Solution 1

Solution 2

Attention! OP changed a tag from C# to C++. I cannot be hold responsible for that. My answer was in C# when the tag was C#. Please do not down-vote based on that.

Solution 3

Solution 5

Solution 4

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