CODEWITHSUNDEEP
c++regex
navig8tr
navig8tr

Reputation: 1844

Find the first instance of multiple strings using regex

Suppose I have a string containing "ATGTTTGGATTAGGTAATGAAT".

I'd like to search the string for the first instance of either "TAG", "TAA", or "TGA".

To do this, I'd like to use regular expressions. I think std::regex_search will work, but I'm unsure how to write the syntax.

Any help would be greatly appreciated.

EDIT: I need to retrieve the position of the first instance of "TAG", "TAA", or "TGA" (whichever comes first).

Upvotes: 2

Views: 921

Answers (4)

Pete Becker
Pete Becker

Reputation: 76345

For this specific problem (that is, assuming that "TAG", "TAA", and "TGA" are the strings to be searched for, and not just representatives of a more general problem), a simple search is easier:

find 'T'
  if the next character is 'A' and the character after that is 'A' or 'G', matched;
  else if the next character is 'G' and the character after that is 'A' matched;
  else go back and try the next 'T'

Upvotes: 0

oldman
oldman

Reputation: 4316

You can try this:

#include <iostream>
#include <regex>

int main() {
    std::string s("ATGTTTGGATTAGGTAATGAAT");
    std::regex r("TAG|TAA|TGA");
    std::sregex_iterator first(s.begin(), s.end(), r);
    std::cout << "position: " << first->position() << std::endl; // position: 10
    return 0;
}

doc is here: http://en.cppreference.com/w/cpp/regex

Upvotes: 3

JawguyChooser
JawguyChooser

Reputation: 1936

I don't know the specific call in c++ (maybe that's what you are asking about), but this is your regex:

/T(A[GA]|GA)/

That is, find a "T" followed by either (an "A" and a ["G" or "A"]) or followed by "GA".

Upvotes: 0

MackC
MackC

Reputation: 350

You can do like this:

#include <iostream>
using namespace std;
int main()
{
    string str="ATGTTTGGATTAGGTAATGAAT";
    string regstr="TAG";
    const char *show;

    show=strstr(str.c_str(), regstr.c_str());//return the pointer of the first place reg 'TAG'，else return NULL。
    cout<<show<<endl;
    return 0;
}

Upvotes: 0

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