Trim a string in C++ – Remove leading and trailing spaces

This post will discuss how to remove leading and trailing spaces from a string in C++. In other words, trim a string in C++.

1. Using `find_first_not_of()` with `find_last_not_of()` function

We can use a combination of string’s find_first_not_of() and find_last_not_of() functions to remove leading and trailing spaces from a string in C++ by finding the index of the first and last non-whitespace character and pass the index to substr() functions to trim the string.

#include <iostream>

#include <string>

#include <algorithm>

const std::string WHITESPACE = " \n\r\t\f\v";

std::string ltrim(const std::string &s)

{

size_t start = s.find_first_not_of(WHITESPACE);

return (start == std::string::npos) ? "" : s.substr(start);

}

std::string rtrim(const std::string &s)

{

size_t end = s.find_last_not_of(WHITESPACE);

return (end == std::string::npos) ? "" : s.substr(0, end + 1);

}

std::string trim(const std::string &s) {

return rtrim(ltrim(s));

}

int main()

{

std::string s = "\n\tHello World \r\n";

std::cout << "START::" << trim(s) << "::END";

return 0;

}

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2. Using `std::find_if` function

Another efficient solution is to use std::find_if to remove leading and trailing spaces, as shown below:

#include <iostream>

#include <string>

#include <algorithm>

std::string& ltrim(std::string &s)

{

auto it = std::find_if(s.begin(), s.end(),

[](char c) {

return !std::isspace<char>(c, std::locale::classic());

});

s.erase(s.begin(), it);

return s;

}

std::string& rtrim(std::string &s)

{

auto it = std::find_if(s.rbegin(), s.rend(),

[](char c) {

return !std::isspace<char>(c, std::locale::classic());

});

s.erase(it.base(), s.end());

return s;

}

std::string& trim(std::string &s) {

return ltrim(rtrim(s));

}

int main()

{

std::string s = "\n\t Hello World ";

std::cout << "START::" << trim(s) << "::END";

return 0;

}

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3. Custom function

We can also write our own routine for this, as shown below:

#include <iostream>

#include <string>

#include <algorithm>

std::string trim(const std::string &s)

{

auto start = s.begin();

while (start != s.end() && std::isspace(*start)) {

start++;

}

auto end = s.end();

do {

end--;

} while (std::distance(start, end) > 0 && std::isspace(*end));

return std::string(start, end + 1);

}

int main()

{

std::string s = "\n\t Hello World \r\n";

std::cout << "START::" << trim(s) << "::END";

return 0;

}

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4. Using `std::regex_replace` function

With C++11, we can also use std::regex_replace for this. This is demonstrated below:

#include <iostream>

#include <string>

#include <regex>

std::string ltrim(const std::string &s) {

return std::regex_replace(s, std::regex("^\\s+"), std::string(""));

}

std::string rtrim(const std::string &s) {

return std::regex_replace(s, std::regex("\\s+$"), std::string(""));

}

std::string trim(const std::string &s) {

return ltrim(rtrim(s));

}

int main()

{

std::string s = " \t\n Hello World ";

std::cout << "START::" << trim(s) << "::END";

return 0;

}

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5. Using Boost Library

Another good alternative is to use Boost Library. It provides trim_right(), trim_left() and trim() functions.

#include <iostream>

#include <string>

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

int main()

{

std::string s = "\n\tHello World \r\n";

boost::algorithm::trim(s);

std::cout << "START::" << s << "::END";

return 0;

}

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That’s all about removing leading and trailing spaces in C++.

Trim a string in C++ – Remove leading and trailing spaces

1. Using find_first_not_of() with find_last_not_of() function

2. Using std::find_if function

3. Custom function

4. Using std::regex_replace function

5. Using Boost Library

Share this:

1. Using `find_first_not_of()` with `find_last_not_of()` function

2. Using `std::find_if` function

4. Using `std::regex_replace` function