Removing leading and trailing spaces from a string

How to remove spaces from a string object in C++.
For example, how to remove leading and trailing spaces from the below string object.

//Original string: "         This is a sample string                    "
//Desired string: "This is a sample string"

The string class, as far as I know, doesn't provide any methods to remove leading and trailing spaces.

To add to the problem, how to extend this formatting to process extra spaces between words of the string. For example,

// Original string: "          This       is         a sample   string    " 
// Desired string:  "This is a sample string"  

Using the string methods mentioned in the solution, I can think of doing these operations in two steps.

1. Remove leading and trailing spaces.
2. Use find_first_of, find_last_of, find_first_not_of, find_last_not_of and substr, repeatedly at word boundaries to get desired formatting.

This is called trimming. If you can use Boost, I'd recommend it.

Otherwise, use find_first_not_of to get the index of the first non-whitespace character, then find_last_not_of to get the index from the end that isn't whitespace. With these, use substr to get the sub-string with no surrounding whitespace.

In response to your edit, I don't know the term but I'd guess something along the lines of "reduce", so that's what I called it. :) (Note, I've changed the white-space to be a parameter, for flexibility)

#include <iostream>
#include <string>

std::string trim(const std::string& str,
                 const std::string& whitespace = " \t")
{
    const auto strBegin = str.find_first_not_of(whitespace);
    if (strBegin == std::string::npos)
        return ""; // no content

    const auto strEnd = str.find_last_not_of(whitespace);
    const auto strRange = strEnd - strBegin + 1;

    return str.substr(strBegin, strRange);
}

std::string reduce(const std::string& str,
                   const std::string& fill = " ",
                   const std::string& whitespace = " \t")
{
    // trim first
    auto result = trim(str, whitespace);

    // replace sub ranges
    auto beginSpace = result.find_first_of(whitespace);
    while (beginSpace != std::string::npos)
    {
        const auto endSpace = result.find_first_not_of(whitespace, beginSpace);
        const auto range = endSpace - beginSpace;

        result.replace(beginSpace, range, fill);

        const auto newStart = beginSpace + fill.length();
        beginSpace = result.find_first_of(whitespace, newStart);
    }

    return result;
}

int main(void)
{
    const std::string foo = "    too much\t   \tspace\t\t\t  ";
    const std::string bar = "one\ntwo";

    std::cout << "[" << trim(foo) << "]" << std::endl;
    std::cout << "[" << reduce(foo) << "]" << std::endl;
    std::cout << "[" << reduce(foo, "-") << "]" << std::endl;

    std::cout << "[" << trim(bar) << "]" << std::endl;
}

Result:

[too much               space]  
[too much space]  
[too-much-space]  
[one  
two]  

Easy removing leading, trailing and extra spaces from a std::string in one line

value = std::regex_replace(value, std::regex("^ +| +$|( ) +"), "$1");

removing only leading spaces

value.erase(value.begin(), std::find_if(value.begin(), value.end(), std::bind1st(std::not_equal_to<char>(), ' ')));

or

value = std::regex_replace(value, std::regex("^ +"), "");

removing only trailing spaces

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

or

value = std::regex_replace(value, std::regex(" +$"), "");

removing only extra spaces

value = regex_replace(value, std::regex(" +"), " ");

I am currently using these functions:

// trim from left
inline std::string& ltrim(std::string& s, const char* t = " \t\n\r\f\v")
{
    s.erase(0, s.find_first_not_of(t));
    return s;
}

// trim from right
inline std::string& rtrim(std::string& s, const char* t = " \t\n\r\f\v")
{
    s.erase(s.find_last_not_of(t) + 1);
    return s;
}

// trim from left & right
inline std::string& trim(std::string& s, const char* t = " \t\n\r\f\v")
{
    return ltrim(rtrim(s, t), t);
}

// copying versions

inline std::string ltrim_copy(std::string s, const char* t = " \t\n\r\f\v")
{
    return ltrim(s, t);
}

inline std::string rtrim_copy(std::string s, const char* t = " \t\n\r\f\v")
{
    return rtrim(s, t);
}

inline std::string trim_copy(std::string s, const char* t = " \t\n\r\f\v")
{
    return trim(s, t);
}

Boost string trim algorithm

#include <boost/algorithm/string/trim.hpp>

[...]

std::string msg = "   some text  with spaces  ";
boost::algorithm::trim(msg);

This is my solution for stripping the leading and trailing spaces ...

std::string stripString = "  Plamen     ";
while(!stripString.empty() && std::isspace(*stripString.begin()))
    stripString.erase(stripString.begin());

while(!stripString.empty() && std::isspace(*stripString.rbegin()))
    stripString.erase(stripString.length()-1);

The result is "Plamen"