is there a way to use cin.getline() without having to define a char array size before hand?

Question

Basically my task is having to sort a bunch of strings of variable length ignoring case. I understand there is a function strcasecmp() that compares cstrings, but doesn't work on strings. Right now I'm using getline() for strings so I can just read in the strings one line at a time. I add these to a vector of strings, then convert to cstrings for each call of strcasecmp(). Instead of having to convert each string to a cstring before comparing with strcasecmp(), I was wondering if there was a way I could use cin.getline() for cstrings without having a predefined char array size. Or, would the best solution be to just read in string, convert to cstring, store in vector, then sort?

Answer 1

I assume by "convert to cstring" you mean using the c_str() member of string. If that is the case, in most implementation that isn't really a conversion, it's just an accessor. The difference is only important if you are worried about performance (which it sounds like you are). Internally std::strings are (pretty much always, but technically do not have to be) represented as a "cstring". The class takes care of managing it's size for you, but it's just a dynamically allocated cstring underneath.

So, to directly answer: You have to specify the size of the array when using cin.getline. If you don't want to specify a size, then use getline and std::string. There's nothing wrong with that approach.

Answer 2

C++ is pretty efficient on its own. Unless you have a truly proven need to do otherwise, let it do its thing.

#include <algorithm>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
#include <cstring>

using namespace std;

bool cmp(string a, string b)
{
    return(strcasecmp(a.c_str(), b.c_str()) < 0);
}  


int main(int argc, char *argv[])
{
    vector<string> strArr;

    //too lazy to test with getline(cin, str);

    strArr.push_back("aaaaa");
    strArr.push_back("AAAAA");
    strArr.push_back("ababab");
    strArr.push_back("bababa");
    strArr.push_back("abcabc");
    strArr.push_back("cbacba");
    strArr.push_back("AbCdEf");
    strArr.push_back("aBcDeF");
    strArr.push_back("  whatever");

    sort(strArr.begin(), strArr.end(), cmp);

    copy(strArr.begin(), strArr.end(), ostream_iterator<string>(cout, " \n"));

    return(0);
}