Removing whitespace from a string variable

Question

So I've looked up various functions and ways to remove whitespaces from strings, but none of them seem to be working for me. Here's what I have right now:

string filename = filenamet;
//remove all whitespace
//filename.erase(remove(filename.begin(), filename.end(), isspace), filename.end());

where filenamet is a string variable, and as is filename. I've double checked all my includes, so they don't seem to be the problem either. Here's the compiler error I'm getting:

test.cpp: In function ‘void input(char*, char**)’:
test.cpp:256:68: error: cannot convert ‘std::basic_string<char>::iterator {aka __gnu_cxx::__normal_iterator<char*, std::basic_string<char> >}’ to ‘const char*’ for argument ‘1’ to ‘int remove(const char*)’ filename.erase(remove(filename.begin(), filename.end(), isspace), filename.end());

I've also tried it with remove_if without remove, but then I get this compiler error:

test.cpp: In function ‘void input(char*, char**)’:
test.cpp:256:71: error: ‘remove_if’ was not declared in this scope
     filename.erase(remove_if(filename.begin(), filename.end(), isspace), filename.end());

Any help is greatly appreciated!

Show the complete compilation error. What are your `#includes` ? — quantdev, Aug 16 '14 at 20:35
possible duplicate of [What's the best way to trim std::string](http://stackoverflow.com/questions/216823/whats-the-best-way-to-trim-stdstring) — Elliott Frisch, Aug 16 '14 at 20:35
@ElliottFrisch OP seems to ask how to delete **all** spaces from a string, not how to trim spaces from the **ends** of a string. So, this is not a duplicate of *that* question. — eerorika, Aug 16 '14 at 20:44

score 3 · Answer 1 · answered Jun 13 '15 at 19:03

Always read your errors carefully!

test.cpp: In function ‘void input(char*, char**)’:
test.cpp:256:68: error: cannot convert 
    ‘std::basic_string<char>::iterator {aka __gnu_cxx::__normal_iterator<char*, std::basic_string<char> >}’ 
     to ‘const char*’ for argument ‘1’ 
     to ‘int remove(const char*)’ 
     filename.erase(remove(filename.begin(), filename.end(), isspace), filename.end());

The issue is that the compiler thinks you're calling this std::remove instead of this std::remove. I'm guessing the issue is that you simply forgot:

#include <algorithm>

because otherwise this line:

filename.erase(remove(filename.begin(), filename.end(), isspace), filename.end());

is the correct way to remove all spaces from the string filename.

Vimal · Answer 2 · 2014-08-17T14:01:06.303

1

You may try this also:

   string::iterator iter = filename.begin();
   while ( iter != filename.end() )
   {
      if ( isspace ( *iter ) )
      {
         iter = filename.erase ( iter );
      }
      else
      {
         iter++;
      }
   }

I compiled and tested it so it should run fine.

edited Aug 17 '14 at 14:01

answered Aug 17 '14 at 12:53

Vimal

436
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I'm afraid that complexity of this might be up to O(n*n). – GingerPlusPlus Jun 13 '15 at 14:36

score 0 · Answer 3 · answered Jun 13 '15 at 14:34

#include <algorithm>
#include <cctype>

// One of this two:

s.resize(std::remove_if(s.begin(), s.end(), std::isspace) - s.begin());
s.erase(std::remove_if(s.begin(), s.end(), std::isspace), s.end());

Explanation

std::remove_if(s.begin(), s.end(), std::isspace) overwrites beggining of the s using s with whitespace characters skipped. It does not change size of string, so if there was any whitespace, end of the s is going to be untouched and contain provious content, which is likely to be useless, so we trim it out using std::string::resize or std::string::erase (std::remove_if return pass-the-end iterator to new content, which I used to determine what to erase / what should be the new size of s).

score -1 · Accepted Answer · answered Aug 16 '14 at 20:47

-1

std::string remove_char(const std::string &input, char to_remove){
    std::string output;
    for(unsigned i=0; i<input.size(); ++i)
        if(input[i]!=to_remove)
            output+=input[i];
    return output;
}

answered Aug 16 '14 at 20:47

GingerPlusPlus

5,336
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1

Actually, you're creating a new string which doesn't contain `to_remove` while that function is supposed to *remove* `to_remove` from `input`. – edmz Aug 17 '14 at 13:52

Removing whitespace from a string variable

4 Answers4

Explanation