Removing leading and trailing spaces from a string

Question

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.

Answer 1

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]