Find and print the number between the parentheses in C++ using Regex -

i using code find number between parentheses in c++.

i want number extracted out huge file contain these type of data:

successful candidates indicated within paranthesis against roll number , marks given [maximum 5 marks] raise grades in hardship cases indicated plus[+] sign , grace marks cases indicated caret[+] sign   600023[545]         600024[554]         600031[605]              600052[560]              ***********  grade : d govt. degree boys college, surjani town   600060[877]         ***********                   ***********                   ***********                   *********** 

///// in 2nd iteration when [554] found. m.size() not reset 0 cause error. how can solve it? how search globally whole file numbers in parenthesis [###]

#include <iostream> #include <fstream> #include <string> #include<conio.h> #include<regex>  using namespace std;  int main () {   ifstream myfile;    myfile.open("test.txt") ;     if(!myfile)  {  cout<<"the file entered not present"<<endl;   }     string str;     if(myfile.is_open())    cout<<"file open";   else       cout<<"file close";  string output;   regex e("\[(\d+)\]");   smatch m;     while (!myfile.eof()) {       myfile >> str;     cout<<"o="<<str<<endl;      bool match=regex_search(str,m,e);      cout<<"m.size() ="<<m.size()<<endl;     int n=0;     for( n=0;n<m.size();n++)     {          cout<<"m["<<n<<"] :str() =" <<m[n].str()<<endl;      }     }    getch();    myfile.close();   return 0; } 

update: able read numbers.using string.

but file huge enough visual studio crashes.

i wanted method searches globally in file.

first, should fix regex e("\[(\d+)\]") regex e("\\[(\\d+)]") (or regex e(r"(\[(\d+)])") if c++ environment supports raw string literals).

then, need obtain multiple matches, not capturing group contents doing. use std::sregex_iterator() , access group 1 contents via m[1].str().

see this c++ demo:

std::regex r("\\[(\\d+)]"); std::string s = "successful candidates indicated within paranthesis against roll number , marks given [maximum 5 marks] raise grades in hardship cases indicated plus[+] sign and\ngrace marks cases indicated caret[+] sign\n\n\n600023[545]         600024[554]         600031[605]              600052[560]              ***********\n\ngrade : d\ngovt. degree boys college, surjani town\n\n\n600060[877]         ***********                   ***********                   ***********                   ***********"; for(std::sregex_iterator = std::sregex_iterator(s.begin(), s.end(), r);                          != std::sregex_iterator();                          ++i) {     std::smatch m = *i;     std::cout << m[1].str() << '\n'; }