How to Remove Spaces From String in C++

1. Use erase-remove Idiom to Remove Spaces From String in C++
2. Use Custom Function to Remove Spaces From String in C++

This article will demonstrate multiple methods about how to remove spaces from a string in C++.

Use erase-remove Idiom to Remove Spaces From String in C++

One of the most useful methods for range manipulation in C++ is the erase-remove idiom which consists of two functions - std::erase (built-in function for the most STL containers) and std::remove (the part of the STL algorithms library). Note that both of them are chained to conduct the removal operation on the given object. std::remove function takes two iterators to specify the range, and the third argument to denote the element’s value to be removed. In this case, we directly specify a space character, but any character can be specified to remove all of its occurrences in the string.

#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl;
using std::string;

int main() {
  string str = "  Arbitrary   str ing with lots of spaces to be removed   .";

  cout << str << endl;

  str.erase(std::remove(str.begin(), str.end(), ' '), str.end());

  cout << str << endl;

  return EXIT_SUCCESS;
}

Output:

Arbitrary   str ing with lots of spaces to be removed   .
Arbitrarystringwithlotsofspacestoberemoved.

On the other hand, the user also can pass unary predicate as the third argument to the std::remove algorithm. The predicate should evaluate to bool value for every element, and when the result is true, the corresponding values are removed from the range. Thus, we can utilize a predefined isspace function that checks for multiple whitespace characters like space - " ", newline - \n, horizontal tab - \t, and several others.

#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl;
using std::string;

int main() {
  string str = "  Arbitrary   str ing with lots of spaces to be removed   .";

  cout << str << endl;

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

  cout << str << endl;

  return EXIT_SUCCESS;
}

Output:

Arbitrary   str ing with lots of spaces to be removed   .
Arbitrarystringwithlotsofspacestoberemoved.

Use Custom Function to Remove Spaces From String in C++

Notice that all previous solutions modified the original string object, but sometimes, one may need to create a new string with all spaces removed. We can implement a custom function using the same erase-remove idiom, that takes the string reference and returns a parsed value to be stored in a separate string object. This method could also be modified to support another function parameter that will specify the character that needs to be removed.

#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl;
using std::string;

string removeSpaces(const string& s) {
  string tmp(s);
  tmp.erase(std::remove(tmp.begin(), tmp.end(), ' '), tmp.end());
  return tmp;
}

int main() {
  string str = "  Arbitrary   str ing with lots of spaces to be removed   .";

  cout << str << endl;

  string newstr = removeSpaces(str);

  cout << newstr << endl;

  return EXIT_SUCCESS;
}

Output:

Arbitrary   str ing with lots of spaces to be removed   .
Arbitrarystringwithlotsofspacestoberemoved.