Using std::search to find multiple occurrence of pattern

Question

I want to use function search or other similar function to find multiple occurrence of given pattern.

This is my code:

#include <cstring>  
#include <iostream> 
#include <iomanip>  
#include <set>
#include <list>
#include <vector>
#include <map>   
#include <algorithm>
#include <functional>
using namespace std;

int main () {
  std::vector<int> haystack;

  string a = "abcabcabc";
  string b = "abc";
  string::iterator it;
  it = search(a.begin(),a.end(),b.begin(),b.end());

  if(it!=a.end()){
      cout << it-a.begin()<<endl;
  }

  return 0;
}

This code return 0 as the first occurrence of pattern "abc" , would like to return 0, 3, 6. That would be all of the indexes in the original string where pattern begins.

Thank you for any help.

possible duplicate of [Find all a substring's occurrences and locations](http://stackoverflow.com/questions/4034750/find-all-a-substrings-occurrences-and-locations) — Cory Kramer, Apr 14 '14 at 13:52
You need a loop, which should finish when `it == a.end()`. What did you try? And is there any particular reason you aren't using `a.find`? — Useless, Apr 14 '14 at 13:53

Danvil · Accepted Answer · 2014-04-14T14:03:13.587

3

for(size_t pos=a.find(b,0); pos!=std::string::npos; pos=a.find(b,pos+1)) {
    std::cout << pos << std::endl;
}

This uses std::basic_string::find (ref) directly to find the starting position of the substring.

edited Apr 14 '14 at 14:03

answered Apr 14 '14 at 13:55

Danvil

22,240
19
65
88

Does this code search a from begining to end everytime ? Or it continues from last position ? – Pastx Apr 14 '14 at 13:59
It continues from `pos+1`. – Danvil Apr 14 '14 at 14:00
What if a case-insensitive search is to be done? In that case, find() will not work. And I am not sure how to advance iterator in search(). Any ideas? – user2761431 Apr 01 '16 at 12:31

score 1 · Answer 2 · answered Apr 14 '14 at 13:55

The search function searches the first string a for any occurence of the elements of the second string b. As Your second string contains the elements a, b and c the code would return an iterator to the first position, then to the second, the third one,...

What You what to use is the find function. It returns an iterator to the element that equals the one that You were searching for. In Your case You're search the string a for the element abc. So You would have to call

string::iterator it = std::find(a.begin(), a.end(), "abc");
while (it != a.end()) {
    // Do whatever you want to do...
    ++it;
    it = std::find(it, a.end(), "abc");
}

score 0 · Answer 3 · answered Jul 08 '21 at 03:40

0

//find first result index
auto find_index = str.find("st");
while(string::npos != find_index) {
  cout << "found at: " << find_index << endl;
  //find next
  find_index = str.find("st",find_index+1);
}

answered Jul 08 '21 at 03:40

LE SANG

10,955
7
59
78

Using std::search to find multiple occurrence of pattern

3 Answers3