Remove spaces from std::string in C++

The best thing to do is to use the algorithm remove_if and isspace:

remove_if(str.begin(), str.end(), isspace);

Now the algorithm itself can't change the container(only modify the values), so it actually shuffles the values around and returns a pointer to where the end now should be. So we have to call string::erase to actually modify the length of the container:

str.erase(remove_if(str.begin(), str.end(), isspace), str.end());

We should also note that remove_if will make at most one copy of the data. Here is a sample implementation:

template<typename T, typename P>
T remove_if(T beg, T end, P pred)
{
    T dest = beg;
    for (T itr = beg;itr != end; ++itr)
        if (!pred(*itr))
            *(dest++) = *itr;
    return dest;
}

std::string::iterator end_pos = std::remove(str.begin(), str.end(), ' ');
str.erase(end_pos, str.end());

From gamedev

string.erase(std::remove_if(string.begin(), string.end(), std::isspace), string.end());

Can you use Boost String Algo? http://www.boost.org/doc/libs/1_35_0/doc/html/string_algo/usage.html#id1290573

erase_all(str, " "); 

   #include <algorithm>
   using namespace std;

   int main() {
       .
       .
       s.erase( remove( s.begin(), s.end(), ' ' ), s.end() );
       .
       .
   }

Source:

Reference taken from this forum.

In C++20 you can use free function std::erase

std::string str = " Hello World  !";
std::erase(str, ' ');

Full example:

#include<string>
#include<iostream>

int main() {
    std::string str = " Hello World  !";
    std::erase(str, ' ');
    std::cout << "|" << str <<"|";
}

I print | so that it is obvious that space at the begining is also removed.

note: this removes only the space, not every other possible character that may be considered whitespace, see https://en.cppreference.com/w/cpp/string/byte/isspace

Removes all whitespace characters such as tabs and line breaks (C++11):

string str = " \n AB cd \t efg\v\n";
str = regex_replace(str,regex("\\s"),"");

string removeSpaces(string word) {
    string newWord;
    for (int i = 0; i < word.length(); i++) {
        if (word[i] != ' ') {
            newWord += word[i];
        }
    }

    return newWord;
}

This code basically takes a string and iterates through every character in it. It then checks whether that string is a white space, if it isn't then the character is added to a new string.

  string str = "2C F4 32 3C B9 DE";
  str.erase(remove(str.begin(),str.end(),' '),str.end());
  cout << str << endl;

output: 2CF4323CB9DE

Just for fun, as other answers are much better than this.

#include <boost/hana/functional/partial.hpp>
#include <iostream>
#include <range/v3/range/conversion.hpp>
#include <range/v3/view/filter.hpp>
int main() {
    using ranges::to;
    using ranges::views::filter;
    using boost::hana::partial;
    auto const& not_space = partial(std::not_equal_to<>{}, ' ');
    auto const& to_string = to<std::string>;

    std::string input = "2C F4 32 3C B9 DE";
    std::string output = input | filter(not_space) | to_string;
    assert(output == "2CF4323CB9DE");
}

I created a function, that removes the white spaces from the either ends of string. Such as " Hello World ", will be converted into "Hello world".

This works similar to strip, lstrip and rstrip functions, which are frequently used in python.

string strip(string str) {
    while (str[str.length() - 1] == ' ') {
        str = str.substr(0, str.length() - 1);
    }
    while (str[0] == ' ') {
        str = str.substr(1, str.length() - 1);
    }
    return str;
}

string lstrip(string str) {
    while (str[0] == ' ') {
        str = str.substr(1, str.length() - 1);
    }
    return str;
}

string rstrip(string str) {
    while (str[str.length() - 1] == ' ') {
        str = str.substr(0, str.length() - 1);
    }
    return str;
}

I'm afraid it's the best solution that I can think of. But you can use reserve() to pre-allocate the minimum required memory in advance to speed up things a bit. You'll end up with a new string that will probably be shorter but that takes up the same amount of memory, but you'll avoid reallocations.

EDIT: Depending on your situation, this may incur less overhead than jumbling characters around.

You should try different approaches and see what is best for you: you might not have any performance issues at all.