How to strip all non alphanumeric characters from a string in c++?

Question

I am writing a piece of software, and It require me to handle data I get from a webpage with libcurl. When I get the data, for some reason it has extra line breaks in it. I

Answer 1

You can use the remove-erase algorithm this way -

// Removes all punctuation       
s.erase( std::remove_if(s.begin(), s.end(), &ispunct), s.end());

Answer 2

The following works for me.

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

Answer 3

Just extending James McNellis's code a little bit more. His function is deleting alnum characters instead of non-alnum ones.

To delete non-alnum characters from a string. (alnum = alphabetical or numeric)

• Declare a function (isalnum returns 0 if passed char is not alnum)

  bool isNotAlnum(char c) {
      return isalnum(c) == 0;
  }
  

• And then write this

  s.erase(remove_if(s.begin(), s.end(), isNotAlnum), s.end());
  

then your string is only with alnum characters.

Answer 4

The mentioned solution

s.erase( std::remove_if(s.begin(), s.end(), &std::ispunct), s.end());

is very nice, but unfortunately doesn't work with characters like 'Ñ' in Visual Studio (debug mode), because of this line:

_ASSERTE((unsigned)(c + 1) <= 256)

in isctype.c

So, I would recommend something like this:

inline int my_ispunct( int ch )
{
    return std::ispunct(unsigned char(ch));
}
...
s.erase( std::remove_if(s.begin(), s.end(), &my_ispunct), s.end());

Answer 5

void remove_spaces(string data)
{ int i=0,j=0;
    while(i<data.length())
    {
        if (isalpha(data[i]))
        {
        data[i]=data[i];
        i++;
        }
        else
            {
            data.erase(i,1);}
    }
    cout<<data;
}