C++ Remove new line from multiline string

Question

Whats the most efficient way of removing a 'newline' from a std::string?

Answer 1

If its anywhere in the string than you can't do better than O(n).

And the only way is to search for '\n' in the string and erase it.

for(int i=0;i<s.length();i++) if(s[i]=='\n') s.erase(s.begin()+i);

For more newlines than:

int n=0;
for(int i=0;i<s.length();i++){
    if(s[i]=='\n'){
        n++;//we increase the number of newlines we have found so far
    }else{
        s[i-n]=s[i];
    }
}
s.resize(s.length()-n);//to delete only once the last n elements witch are now newlines

It erases all the newlines once.

Answer 2

If the newline is expected to be at the end of the string, then:

if (!s.empty() && s[s.length()-1] == '\n') {
    s.erase(s.length()-1);
}

If the string can contain many newlines anywhere in the string:

std::string::size_type i = 0;
while (i < s.length()) {
    i = s.find('\n', i);
    if (i == std::string:npos) {
        break;
    }
    s.erase(i);
}

Answer 3

You should use the erase-remove idiom, looking for '\n'. This will work for any standard sequence container; not just string.

Answer 4

Use std::algorithms. This question has some suitably reusable suggestions Remove spaces from std::string in C++

Answer 5

s.erase(std::remove(s.begin(), s.end(), '\n'), s.end());

Answer 6

The code removes all newlines from the string str.

O(N) implementation best served without comments on SO and with comments in production.

unsigned shift=0;
for (unsigned i=0; i<length(str); ++i){
    if (str[i] == '\n') {
        ++shift;
    }else{
        str[i-shift] = str[i];
    }
}
str.resize(str.length() - shift);

Answer 7

#include <algorithm>
#include <string>

std::string str;

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

The behavior of std::remove may not quite be what you'd expect. See an explanation of it here.

Answer 8

 std::string some_str = SOME_VAL;
 if ( some_str.size() > 0 && some_str[some_str.length()-1] == '\n' ) 
  some_str.resize( some_str.length()-1 );

or (removes several newlines at the end)

some_str.resize( some_str.find_last_not_of(L"\n")+1 );

Answer 9

All these answers seem a bit heavy to me.

If you just flat out remove the '\n' and move everything else back a spot, you are liable to have some characters slammed together in a weird-looking way. So why not just do the simple (and most efficient) thing: Replace all '\n's with spaces?

for (int i = 0; i < str.length();i++) {
   if (str[i] == '\n') {
      str[i] = ' ';
   }
}

There may be ways to improve the speed of this at the edges, but it will be way quicker than moving whole chunks of the string around in memory.