How to find occurrences of a string in string in C++?

Question

Here is the Scenario.

string base_string = "BF;1;2;3;FF;10;20;30;BF;11;;22;33;FF;100;200;300;BF;110;;220;330;FF;1000;2000;3000";
string to_find_occurances_of = "BF";

@BjörnPollex Removed the tag #c-strings – DreamCodeer Dec 23 '11 at 10:01 — DreamCodeer, Dec 23 '11 at 10:01

score 23 · Accepted Answer · edited Jun 30 '14 at 13:29

int occurrences = 0;
string::size_type start = 0;

while ((start = base_string.find(to_find_occurrences_of, start)) != string::npos) {
    ++occurrences;
    start += to_find_occurrences_of.length(); // see the note
}

string::find takes a string to look for in the invoking object and (in this overload) a character position at which to start looking, and returns the position of the occurrence of the string, or string::npos if the string is not found.

The variable start starts at 0 (the first character) and in the condition of the loop, you use start to tell find where to start looking, then assign the return value of find to start. Increment the occurrence count; now that start holds the position of the string, you can skip to_find_occurrences_of.length()¹ characters ahead and start looking again.

¹ drhirsch makes the point that if to_find_occurrences_of contains a repeated sequence of characters, doing start += to_find_occurrences_of.length() may skip some occurrences. For instance, if base_string was "ffff" and to_find_occurrences_of was "ff", then only 2 occurrences would be counted if you add to_find_occurrences_of.length() to start. If you want to avoid that, add 1 instead of to_find_occurrences_of.length() to start, and in that example, 3 occurrences would be counted instead of just 2.

You will skip some "occurances" if _to_find_occurances_of_ consists of repeated characters or sequences. — Gunther Piez, Dec 23 '11 at 09:27
@DreamCodeer forgive me if you already know this, but if this answer answered your question, please mark it as answered by clicking the checkmark beside the answer. — Seth Carnegie, Dec 23 '11 at 09:33
Great! What must I do to make it works, no matter small or capital letters? — IntoTheDeep, Apr 09 '17 at 21:04

score 2 · Answer 2 · edited Aug 01 '13 at 03:55

Here the code to find string occurance in string with user defined Find function

int Find(char OrgStr[], char szFind[]);

void main(){
   int iCount = Find("babbabaab ab", "ab");
   //cout<<"No of 'abe' : " << iCount <<endl;

}

int Find(char orgStr[], char findStr[]){    
    int i,j,k,l,szLen,orgLen;
    char temp[] = " ";

    orgLen = strlen(orgStr);
    szLen = strlen(findStr); 

    k= 0;
    i = 0;
    l = 0;

    while( l < orgLen )
    {
        i = (orgLen - ( orgLen - l));
        for( j = 0; j < szLen; j++)
        {
            temp[j] = orgStr[i];            
            i++;
        }
        temp[j] = '\0';
        if(strcmp(temp,findStr) == 0)
        {
            k++;
        }
        strcpy(temp,"");
        l++;
    }
    cout<<"No of 'ab' : " << k <<endl;
    return k;
    //strcpy(temp,"");
}

score 2 · Answer 3 · answered Jul 30 '18 at 02:25

You can use the Boost C++ library in this case. Here is an example of string matching:

#include <boost/algorithm/string.hpp>
#include <string>
#include <iostream>
#include <vector>

using StringRange = boost::iterator_range<std::string::const_iterator>;

int main()
{
    std::string base_string = "BF;1;2;3;FF;10;20;30;BF;11;;22;33;FF;100;200;300;BF;110;;220;330;FF;1000;2000;3000";
    std::string to_find_occurances_of = "BF";

    std::vector<StringRange> matches;
    boost::find_all(matches, base_string, to_find_occurances_of);
    for (auto match : matches) {
        std::cout << "Found [" << to_find_occurances_of << "] at index " << match.begin() - base_string.begin() << ".\n";
    }
}

This code prints:

Found [BF] at index 0.
Found [BF] at index 21.
Found [BF] at index 49.

score 1 · Answer 4 · edited Feb 26 '15 at 03:14

1

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

int main ()
{
      string str("BF;1;2;3;FF;10;20;30;BF;11;;22;33;FF;100;200;300;BF;110;;220;330;FF;1000;2000;3000");
      string str2 ("BF");
      size_t found;

      // different member versions of find in the same order as above:
      found=str.find(str2);
//print

            return 0;
}

edited Feb 26 '15 at 03:14

Uli Köhler

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answered Dec 23 '11 at 09:25

jiten

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Thanks. Have used the first one. – DreamCodeer Dec 23 '11 at 10:04
What is size_t here? – Krish Munot Aug 25 '16 at 05:56

How to find occurrences of a string in string in C++?

4 Answers4