Convert std::vector to std::string without \0-CodePudding

I want to remove the vowels from a std::string with this code:

# include <string>
#include <vector>

bool IsVowel(char c) {
    return ((c == 'a') ||
        (c == 'A') ||
        (c == 'e') ||
        (c == 'E') ||
        (c == 'i') ||
        (c == 'I') ||
        (c == 'o') ||
        (c == 'O') ||
        (c == 'u') ||
        (c == 'U'));
}

std::string RemoveVowel(const std::string& str) {
    const size_t s = str.length();

    std::vector<char> inProgress(s);

    int index = 0;
    for (char c : str) {
        if (!IsVowel(c)) {
            inProgress[index] = c;
            index  ;
        }
    }

    std::string sy(inProgress.begin(), inProgress.end());
    return sy;

}

But with this input:

"aaaaaa"

I get this output:

"\0\0\0\0\0\0"

But I want to get this:

""

The problem is with std::string sy(inProgress.begin(), inProgress.end());. I don't know how to convert the std::vector to std::string without any \0.

How can I fix this problem?

CodePudding user response：

As you can see, inProgress always contains str.length() many elements. index tells you the actual number of vowels in there. std::string has constructors that let you use that information to determine how much of inProgress to use in the initialization of sy.

So, you could do:

std::string sy(inProgress.begin(), inProgress.begin()   index);
return sy;

This would construct sy using only the initial segment of inProgress that actually contains vowels.

CodePudding user response：

The answer by Nathan Pierson explains how to do what you want.

But there are easier ways:

C 20 or newer:

std::string RemoveVowel(std::string str)
{
    std::erase_if(str, IsVowel);
    return str;
}

C 17:

std::string RemoveVowel(std::string_view str)
{
    std::string ret;
    ret.reserve(str); // Optional.
    std::copy_if(str.begin(), str.end(), std::back_inserter(ret), std::not_fn(IsVowel));
    return ret;
}

C 14 and earlier:

std::string RemoveVowel(const std::string &str)
{
    std::string ret;
    ret.reserve(str); // Optional.
    std::copy_if(str.begin(), str.end(), std::back_inserter(ret), [](char ch){return !IsVowel(ch);});
    return ret;
}

Even if you don't want to keep the custom loop, you should replace std::vector with a std::string to avoid the extra copy at the return.

CodePudding user response：

You could not pass in an initial size for your vector and use push_back:

std::string RemoveVowel(const std::string& str) {
  std::vector<char> in_progress;
  in_progress.reserve(str.size());
  for (const char& c : str) {
    if (!IsVowel(c)) {
      in_progress.push_back(c);
    }
  }
  std::string sy(in_progress.begin(), in_progress.end());
  return sy;
}

Or alternatively use a stringstream instead:

std::string RemoveVowel(const std::string& str) {
  std::stringstream ss;
  for (const char& c : str) {
    if (!IsVowel(c)) {
      ss << c;
    }
  }
  return ss.str();
}

CodePudding user response：

Instead, use std::vector::push_back(value) to insert new valid characters into your vector, rather than setting null values.

for (char c : str) {
    if (!IsVowel(c)) {
        inProgress.push_back(c);
    }
}
std::string sy(inProgress.begin(), inProgress.end());
return sy;

Alternatively, can't you simply just append to an output string?

std::string sy = "";
for (char c : str) {
    if (!IsVowel(c)) {
        sy  = c;
    }
}
return sy;