c++ - extract digits from filename -

i working file-names in c++. need know how extract part of file-name? file-names like:

/home/xyz/123b45.dat  /home/xyz/012b06c.dat  /home/xyz/103b12d.dat  /home/xyz/066b50.dat 

i want extract 2 digits after 'b' (45, 06, 12, 50) each file-name , store in array. please suggest how it...

use std::string::find , std::string::substr:

int main() {     std::string line;     std::vector<std::string> parts;     while (std::getline(std::cin, line))     {         auto suffix = line.find(".dat");         if ( suffix != std::string::npos && suffix >= 2)         {             std::string part = line.substr(suffix-2, 2);             parts.push_back(part);         }     }      ( auto & s : parts )         std::cout << s << '\n';      return 0; } 

ouput input:

$ ./a.out < inp 45 06 12 50 

or, if absolutely sure every single line formed, replace inside of loop with:

std::string part = line.substr(line.size()-6, 2); parts.push_back(part); 

(not recommended).

edit: noticed changed criteria of question, here's replacement loop new criteria:

auto bpos = line.find_last_of('b'); if ( bpos != std::string::npos && line.size() >= bpos+2) {     std::string part = line.substr(bpos+1, 2);     parts.push_back(part); } 

note of these variations have same output.

you chuck isdigit in there measure too.

final edit: full bpos version, c++98 compatible:

#include <iostream> #include <vector> #include <string>  int main() {     std::string line;     std::vector<std::string> parts;     // read available lines.     while (std::getline(std::cin, line))     {         // find last 'b' in line.         std::string::size_type bpos = line.find_last_of('b');         // make sure line reasonable         // (has 'b' , @ least 2 characters after)         if ( bpos != std::string::npos && line.size() >= bpos+2)         {             // 2 characters after 'b', std::string.             std::string part = line.substr(bpos+1, 2);             // push onto vector.             parts.push_back(part);         }     }      // prints out vector example,     // can safely ignore it.     std::vector<std::string>::const_iterator = parts.begin();     ( ; != parts.end(); ++it )         std::cout << *it << '\n';      return 0; }