Remove spaces from a string in C++ - c++

Question

I am currently learning C++. I am trying to code a method to remove white spaces form a string and return the string with no spaces
This is my code:
string removeSpaces(string input)
{
int length = input.length();
for (int i = 0; i < length; i++) {
if(input[i] == ' ')
input.erase(i, 1);
}
return input
}
But this has a bug as it won't remove double or triple white spaces.
I found this on the net
s.erase(remove(s.begin(),s.end(),' '),s.end());
but apparently this is returning an iterator (if I understand well)
Is there any way to convert the iterator back to my string input?
Most important is this the right approach?

Answer 1

std::string::erase returns an iterator, but you don't have to use it. Your original string is modified.
string removeSpaces(string input)
{
input.erase(std::remove(input.begin(),input.end(),' '),input.end());
return input;
}

Answer 2

std::remove_if along with erase would be much easier (see it live):
input.erase(remove_if(input.begin(), input.end(), isspace),input.end());
using std::isspace had the advantage it will capture all types of white space.

Answer 3

Let's assume your input has a double space, for example "c++[ ][ ]is[ ]fun" ([ ] represents a single space). The first space has index 3 (numeration starts from 0) and the second space, is of course index 4.
In your for loop, when you hit i == 3 you erase the first space. The next iteration of the loop takes i == 4 as the index. But is the second space at index 4 now ? No! Removing the first space changed the string into "c++[ ]is[ ]fun": the space to remove is at index 3, again!
The solution can be to remove spaces right-to-left:
for (int i = length-1; i >= 0; --i) {
if(input[i] == ' ')
input.erase(i, 1);
}
This solution has the benefit of being simple, but as Tony D points out, it's not efficient.

Answer 4

this should also work -- std::replace( input.begin(), input.end(), ' ', ''); You need to include <algorithm>

Answer 5

this code should work
string removeSpaces(string input)
{
int length = input.length();
for (int i = 0; i < length; i++) {
if(input[i] == ' ')
{
input.erase(i, 1);
length--;
i--;
}
}
return input
}
Reason: if it gets space in the string it will reduce the length of the string, so you have to change the variable: "length" accordingly.

Answer 6

I tried to write something to.
This function take a string and copy to another temporary string all the content without extra spaces.
std::string trim(std::string &str){
int i = 0;
int j = 0;
int size = str.length();
std::string newStr;
bool spaceFlag = false;
for(int i = 0;i < size; i++){
if(str[i] == ' ' && (i+1) < size && str[i+1] == ' '){
i++;
spaceFlag = true;
continue;
}
if(str[i] == ' '){
newStr += " ";
continue;
}
if(str[i] == '\t' && i != 0){
str[i] = ' ';
newStr += " ";
}
else{
newStr += str[i];
if(spaceFlag){
newStr += " ";
spaceFlag = false;
}
}
}
str = newStr;
return str;
}

Answer 7

#include<iostream>
#include<string.h>
using namespace std;
void trimSpace(char s[])
{
int i=0, count=0, j=0;
while(s[i])
{
if(s[i]!=' ')
s[count++]=s[i++];
else {
s[count++]=' ';
while(s[i]==' ')
i++;
}
}
s[count]='\0';
cout<<endl<<" Trimmed String : ";
puts(s);
}
int main()
{
char string[1000];
cout<<" Enter String : ";
gets(string);
trimSpace(string);
return 0;
}