如何在C ++中将某些字符复制到字符串中

Question

In one part of my code I should get characters one by one. It's easy but my question is how can I add these characters one by one into a string. Note that I don't know how many characters I will get. It is important that just the characters be copied in string. In the other words, I want to generate words from characters until the character is not equal to ' ' or '\\n' . the wrong code that I wrote is:

 char c;
 string str = NULL;
 cin.get(c);
 while (c != " ")
 {
      str += c;
      cin.get(c);
 }
 cout << str ; 

For example, if character c would be 'H' at first and then be 'i' , I want to the string str to be "Hi" on cout !

Answer 1

=! should be != , and the string " " should be a character ' ' .

If you want to check for new-line characters as well as space:

while (c != ' ' && c != '\n')

or perhaps

while (!std::isspace(c))

which will read up to any whitespace character.

You should also check for the end of the stream or other problems:

while (cin.get(c) && !std::isspace(c)) {
    str += c;
}

Answer 2

如果您只想阅读直到空格或换行符：

std::getline( cin, str, ' ' );

Answer 3

c++ stringstreams are also useful when building strings

stringstream ss;
while (cin.get(c) && !std::isspace(c)) {
    ss << c;
}
string s = ss.str();
cout << s;

Answer 4

The mistake in your code was that you weren't checking for the newline character. Also, it should have been != instead of =! . The second option will actually behave as c = (!(" ")) in your code. Another mistake is that you should be checking for the blank space character ' ' instead of an empty string " " .

Here is the correct code:

char c;
string str = "";
while (true)
{
     cin.get(c);
     cout << "c is " << c << endl;       
         if ((c == ' ') || (c == '\n'))
     break;
     str += c;
}
cout << str << endl ; 

Also, if your requirement is that the I/O be stopped the moment a space character is encountered, refer to this question: C - Reading from stdin as characters are typed

All the solutions proposed here will continue to read input until the new line character is entered because until then your input hasn't been processed, but instead stored in a buffer.

Answer 5

If your str starts out empty, this is simple:

string str;

cin >> str; // cin's >> operator already reads until whitespace

cout << str;

Answer 6

If you don't know in advance how many characters it would be, I would declare a std::list, push elements to it and then copy them into a string. This ensures that you don't reallocate the string memory on every addition:

char c;
list<char> buff;
cin.get(c);
while (c != ' ' && c != '\n')
{
    buff.push_back (c);
    cin.get(c);
}
string str (buff.size(), 0);
size_t i = 0;
while (!buff.empty())
{
    str[i] = buff.front();
    buff.pop_front();
    ++i;
}
cout << str ;