How to remove all the occurrences of a char in c++ string

I am using following:

replace (str1.begin(), str1.end(), 'a' , '')

But this is giving compilation error.

Basically, replace replaces a character with another and '' is not a character. What you're looking for is erase.

See this question which answers the same problem. In your case:

#include <algorithm>
str.erase(std::remove(str.begin(), str.end(), 'a'), str.end());

Or use boost if that's an option for you, like:

#include <boost/algorithm/string.hpp>
boost::erase_all(str, "a");

All of this is well-documented on reference websites. But if you didn't know of these functions, you could easily do this kind of things by hand:

std::string output;
output.reserve(str.size()); // optional, avoids buffer reallocations in the loop
for(size_t i = 0; i < str.size(); ++i)
  if(str[i] != 'a') output += str[i];

The algorithm std::replace works per element on a given sequence (so it replaces elements with different elements, and can not replace it with nothing). But there is no empty character. If you want to remove elements from a sequence, the following elements have to be moved, and std::replace doesn't work like this.

You can try to use std::remove() together with str.erase()1 to achieve this.

str.erase(std::remove(str.begin(), str.end(), 'a'), str.end());

Using copy_if:

#include <string>
#include <iostream>
#include <algorithm>
int main() {
    std::string s1 = "a1a2b3c4a5";
    std::string s2;
    std::copy_if(s1.begin(), s1.end(), std::back_inserter(s2),
         [](char c){ 
                std::string exclude = "a";
                return exclude.find(c) == std::string::npos;}
    );

    std::cout << s2 << '\n';
    return 0;
}

string RemoveChar(string str, char c) 
{
   string result;
   for (size_t i = 0; i < str.size(); i++) 
   {
	      char currentChar = str[i];
	      if (currentChar != c)
		      result += currentChar;
   }
       return result;
}

This is how I did it.

Or you could do as Antoine mentioned:

> See this > question > which answers the same problem. In your case: > > #include > str.erase(std::remove(str.begin(), str.end(), 'a'), str.end());

Starting with C++20, std::erase() has been added to the standard library, which combines the call to str.erase() and std::remove() into just one function:

std::erase(str, 'a');

The std::erase() function overload acting on strings is defined directly in the <string> header file, so no separate includes are required. Similiar overloads are defined for all the other containers.

This code removes repetition of characters i.e, if the input is aaabbcc then the output will be abc. (the array must be sorted for this code to work)

cin >> s;
ans = "";
ans += s[0];
for(int i = 1;i < s.length();++i)
if(s[i] != s[i-1])
    ans += s[i];
cout << ans << endl;

In case you have a predicate and/or a non empty output to fill with the filtered string, I would consider:

output.reserve(str.size() + output.size());  
std::copy_if(str.cbegin(), 
             str.cend(), 
             std::back_inserter(output), 
             predicate});

In the original question the predicate is [](char c){return c != 'a';}

Based on other answers, here goes one more example where I removed all special chars in a given string:

#include <iostream>
#include <string>
#include <algorithm>

std::string chars(".,?!.:;_,!'\"-");

int main(int argc, char const *argv){

  std::string input("oi?");
  std::string output = eraseSpecialChars(input);   
    
 return 0;
}




std::string eraseSpecialChars(std::string str){

std::string newStr;
    newStr.assign(str);  

    for(int i = 0; i < str.length(); i++){
        for(int  j = 0; j < chars.length(); j++ ){
            if(str.at(i) == chars.at(j)){
                char c = str.at(i);
                newStr.erase(std::remove(newStr.begin(), newStr.end(), c), newStr.end());
            }
        }
          
    }      

return newStr; 
}

Input vs Output:

Input:ra,..pha
Output:rapha

Input:ovo,
Output:ovo

Input:a.vo
Output:avo

Input:oi?
Output:oi

I have a string being read:

"\"internet\""

and I want to remove the quotes. I used the std::erase solution suggested above:

str.erase(std::remove(str.begin(), str.end(), '\"'), str.end());

but when I then did a compare on the result it failed:

if (str == "internet") {}

What I actually got was:

"internet "

The std::erase / std::remove solution doesn't shorten the string when it removes the end. I added this (from https://stackoverflow.com/a/21815483/264822):

str.erase(std::find_if(str.rbegin(), str.rend(), std::bind1st(std::not_equal_to<char>(), ' ')).base(), str.end());

to remove the trailing space(s).

I guess the method std:remove works but it was giving some compatibility issue with the includes so I ended up writing this little function:

string removeCharsFromString(const string str, char* charsToRemove )
{
    char c[str.length()+1]; // + terminating char
    const char *p = str.c_str();
    unsigned int z=0, size = str.length();
    unsigned int x;
    bool rem=false;

    for(x=0; x<size; x++)
    {
        rem = false;
        for (unsigned int i = 0; charsToRemove[i] != 0; i++)
        {
            if (charsToRemove[i] == p[x])
            {
                rem = true;
                break;
            }
        }
        if (rem == false) c[z++] = p[x];
    }

    c[z] = '\0';
    return string(c);
}

Just use as

> myString = removeCharsFromString(myString, "abc\r");

and it will remove all the occurrence of the given char list.

This might also be a bit more efficient as the loop returns after the first match, so we actually do less comparison.

This is how I do it:

std::string removeAll(std::string str, char c) {
	size_t offset = 0;
	size_t size = str.size();

	size_t i = 0;
	while (i < size - offset) {
		if (str[i + offset] == c) {
			offset++;
		}
		
		if (offset != 0) {
			str[i] = str[i + offset];
		}

		i++;
	}

    str.resize(size - offset);
	return str;
}

Basically whenever I find a given char, I advance the offset and relocate the char to the correct index. I don't know if this is correct or efficient, I'm starting (yet again) at C++ and i'd appreciate any input on that.

70% Faster Solution than the top answer

		void removeCharsFromString(std::string& str, const char* charsToRemove)
		{
            size_t charsToRemoveLen = strlen(charsToRemove);
			std::remove_if(str.begin(), str.end(), [charsToRemove, charsToRemoveLen](char ch) -> bool
				{
					for (int i = 0; i < charsToRemoveLen; ++i) {
						if (ch == charsToRemove[i])
							return true;
					}
					return false;
				});
		}

#include <string>
#include <algorithm>
std::string str = "YourString";
char chars[] = {'Y', 'S'};
str.erase (std::remove(str.begin(), str.end(), chars[i]), str.end());

Will remove capital Y and S from str, leaving "ourtring".

Note that remove is an algorithm and needs the header <algorithm> included.