Is there any function in C++ std::string that count total number of same starting characters of two strings or any best way to do

Question

Eg.

abcfgf
abdef

ans=2 {"ab" is a common starting character}

There's nothing with asking precise questions like this, imho. We should all strive to maximise our use of standard library functions. — Bathsheba, May 13 '17 at 13:26
Possible duplicate of [Check if one string is a prefix of another](http://stackoverflow.com/questions/7913835/check-if-one-string-is-a-prefix-of-another) — CroCo, May 13 '17 at 18:39
@πάνταῥεῖ: Except, the C++ Standard Library does provide such a function. You have to be very careful when claiming something doesn't exist. — Ben Voigt, May 14 '17 at 05:38

score 12 · Answer 1 · answered May 13 '17 at 13:32

12

You could use std::mismatch, which returns a pair of iterators indicating the respective iterators where sequences start to differ.

To count the length of common prefixes, for example, you could do the following:

#include <iostream>                                                                                                                                                                                         
#include <iterator>
#include <string>
#include <algorithm>
using namespace std;

int main() {
    const string l = "abcde", r = "abcdfgh";
    cout << distance(begin(l), mismatch(begin(l), end(l), begin(r)).first) << endl;
}

answered May 13 '17 at 13:32

Ami Tavory

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@Bathsheba :-) Thanks – Ami Tavory May 13 '17 at 13:33
Learned something new today. This should be the accepted answer! – gsamaras May 13 '17 at 13:36
@AmiTavory it shows error: 'begin' was not declared in this scope| error: 'end' was not declared in this scope| – r_ranjan May 13 '17 at 18:42
@r_ranjan Are you compiling this in c++11 mode? In any case, you could switch `begin(l)` with `l.begin()`. – Ami Tavory May 13 '17 at 18:49

score 1 · Answer 2 · edited May 23 '17 at 10:31

It seems that there is a buildin function to do this, as shown in this answer.

However, you could do it by simply using a loop (if you want, but would not suggest it), like this:

#include <iostream>
#include <string>

using namespace std;

int main()
{
    string str1 = "abcfgf";
    string str2 = "abdet";

    int counter = 0;

    for(int i = 0; i < str1.size() && i < str2.size(); ++i)
        if(str1[i] == str2[i])
            counter++;

    cout << counter << endl;
    return 0;
}

Output:

2

Is there any function in C++ std::string that count total number of same starting characters of two strings or any best way to do

2 Answers2