在字符串上使用 getline

Question

How can I use getline() to read words form a line that I have stored in a string?

For example:

char ch[100],w[20];
cin.getline(ch,100);

Now can I use getline to count the number of words in ch ? I don't want to use a delimiter to directly count words from ch . I want to read words from ch and store them in w .

I have tried using ch in getline as a parameter.

Answer 1

getline is implemented in the standard as either a stream method , or a string method which takes a stream: http://en.cppreference.com/w/cpp/string/basic_string/getline

There is no standard implementation of getline which does not require a stream.

That said you can use ch to seed a istringstream to count the words in the string, but basic_istream<CharT, Traits>& getline(basic_istream<CharT, Traits>&& input, basic_string<CharT, Traits, Allocator>& str) assumes a newline as the delimiter so that's not what you're going to want to count words. Similarly, a getline that takes a delimiter will only break on a specific character. Instead you could usebasic_istream& basic_istream::operator>> which will split words on all whitespace characters:

istringstream foo(ch);

for(auto i = 1; foo >> w; ++i) {
    cout << i << ": " << w << endl;
}

Live Example

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Just as a note here, defining char w[20] is just begging for an out of bounds write. At a minimum you need to define that such that if ch is filled with non-whitespace characters, w can contain it all. You could do that by defining char w[100] .
But if someone were to come and increase the size of ch without changing the size of w and then you'd be in trouble again. In C++17 you could define w like this char w[size(ch)] prior to that you could do char w[sizeof(ch) / sizeof(ch[0])]
But your best option is probably to just make both w and ch string s so they can dynamically resize to accommodate user input.