Remove spaces from std::string in C++

c++ string stl whitespace
Steve Hanov picture Steve Hanov · Sep 17, 2008 · Viewed 375.5k times · Source

What is the preferred way to remove spaces from a string in C++? I could loop through all the characters and build a new string, but is there a better way?

Answer

Matt Price picture Matt Price · Sep 17, 2008

The best thing to do is to use the algorithm remove_if and isspace:

remove_if(str.begin(), str.end(), isspace);

Now the algorithm itself can't change the container(only modify the values), so it actually shuffles the values around and returns a pointer to where the end now should be. So we have to call string::erase to actually modify the length of the container:

str.erase(remove_if(str.begin(), str.end(), isspace), str.end());

We should also note that remove_if will make at most one copy of the data. Here is a sample implementation:

template<typename T, typename P>
T remove_if(T beg, T end, P pred)
{
    T dest = beg;
    for (T itr = beg;itr != end; ++itr)
        if (!pred(*itr))
            *(dest++) = *itr;
    return dest;
}

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