C++ Remove punctuation from String

Question

I got a string and I want to remove all the punctuations from it. How do I do that? I did some research and found that people use the ispunct() function (I tried that), but

Answer 1

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

int main() {
    string str = "this. is my string. it's here.";

    transform(str.begin(), str.end(), str.begin(), [](char ch)
    {
        if( ispunct(ch) )
            return '\0';
        return ch;
    });
}

Answer 2

Another way you could do this would be as follows:

#include <ctype.h> //needed for ispunct()
string onlyLetters(string str){
    string retStr = "";

    for(int i = 0; i < str.length(); i++){
        if(!ispunct(str[i])){
            retStr += str[i];
        }
    }
    return retStr;

This ends up creating a new string instead of actually erasing the characters from the old string, but it is a little easier to wrap your head around than using some of the more complex built in functions.

Answer 3

i got it.

size_t found = text.find('.');
text.erase(found, 1);

Answer 4

The problem here is that ispunct() takes one argument being a character, while you are trying to send a string. You should loop over the elements of the string and erase each character if it is a punctuation like here:

for(size_t i = 0; i<text.length(); ++i)
  if(ispunct(text[i]))
    text.erase(i--, 1);

Answer 5

Try to use this one, it will remove all the punctuation on the string in the text file oky. str.erase(remove_if(str.begin(), str.end(), ::ispunct), str.end());

please reply if helpful

Answer 6

POW already has a good answer if you need the result as a new string. This answer is how to handle it if you want an in-place update.

The first part of the recipe is std::remove_if, which can remove the punctuation efficiently, packing all the non-punctuation as it goes.

std::remove_if (text.begin (), text.end (), ispunct)

Unfortunately, std::remove_if doesn't shrink the string to the new size. It can't because it has no access to the container itself. Therefore, there's junk characters left in the string after the packed result.

To handle this, std::remove_if returns an iterator that indicates the part of the string that's still needed. This can be used with strings erase method, leading to the following idiom...

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

I call this an idiom because it's a common technique that works in many situations. Other types than string provide suitable erase methods, and std::remove (and probably some other algorithm library functions I've forgotten for the moment) take this approach of closing the gaps for items they remove, but leaving the container-resizing to the caller.