remove whitespace in std::string

Question

In C++, what's an easy way to turn:

This std::string

\t\tHELLO WORLD\r\nHELLO\t\nWORLD     \t

Into:

HELLOWORLDHELLOWORLD

Answer 1

Simple combination of std::remove_if and std::string::erase.

Not totally safe version

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

For safer version replace ::isspace with

std::bind( std::isspace<char>, _1, std::locale::classic() )

(Include all relevant headers)

For a version that works with alternative character types replace <char> with <ElementType> or whatever your templated character type is. You can of course also replace the locale with a different one. If you do that, beware to avoid the inefficiency of recreating the locale facet too many times.

In C++11 you can make the safer version into a lambda with:

[]( char ch ) { return std::isspace<char>( ch, std::locale::classic() ); }

Answer 2

If C++03

struct RemoveDelimiter
{
  bool operator()(char c)
  {
    return (c =='\r' || c =='\t' || c == ' ' || c == '\n');
  }
};

std::string s("\t\tHELLO WORLD\r\nHELLO\t\nWORLD     \t");
s.erase( std::remove_if( s.begin(), s.end(), RemoveDelimiter()), s.end());

Or use C++11 lambda

s.erase(std::remove_if( s.begin(), s.end(), 
     [](char c){ return (c =='\r' || c =='\t' || c == ' ' || c == '\n');}), s.end() );

PS. Erase-remove idiom is used

Answer 3

c++11

std::string input = "\t\tHELLO WORLD\r\nHELLO\t\nWORLD     \t";

auto rs = std::regex_replace(input,std::regex("\\s+"), "");

std::cout << rs << std::endl;

/tmp ❮❮❮ ./play

HELLOWORLDHELLOWORLD

Answer 4

In C++11 you can use a lambda rather than using std::bind:

str.erase(
    std::remove_if(str.begin(), str.end(), 
        [](char c) -> bool
        { 
            return std::isspace<char>(c, std::locale::classic()); 
        }), 
    str.end());

Answer 5

You could use Boost.Algorithm's erase_all

#include <boost/algorithm/string/erase.hpp>
#include <iostream>
#include <string>

int main()
{
    std::string s = "Hello World!";
    // or the more expensive one-liner in case your string is const
    // std::cout << boost::algorithm::erase_all_copy(s, " ") << "\n";
    boost::algorithm::erase_all(s, " "); 
    std::cout << s << "\n";
}

NOTE: as is mentioned in the comments: trim_copy (or its cousins trim_copy_left and trim_copy_right) only remove whitespace from the beginning and end of a string.

Answer 6

Stepping through it character by character and using string::erase() should work fine.

void removeWhitespace(std::string& str) {
    for (size_t i = 0; i < str.length(); i++) {
        if (str[i] == ' ' || str[i] == '\n' || str[i] == '\t') {
            str.erase(i, 1);
            i--;
        }
    }
}