c++ - compare two maps and identify distinct elements -

compare 2 maps (std::map<std::string, std::unsigned int>) value , identify distinct elements.

typedef std::map<std::string /* file name*/, unsigned int /*crc*/> mmap; 

list of files each file in list calculated crc. file name not changed, crc changet.

if have 2 maps, distinct entries, named oldmap , newmap, can use std::set_difference unique entries both maps. see following example of how can done.

#include <map> #include <string> #include <algorithm> #include <utility> #include <iterator> #include <iostream>  int main() {     // 2 maps containing values.     std::map<std::string, int> oldmap { {"test1", 1}, {"test2", 2}, {"test3", 3} };     std::map<std::string, int> newmap { {"test2", 2} };      // create new map holds distinct pairs.     std::map<std::string, int> diffmap;      // add distinct pairs diffmap.     std::set_difference(begin(oldmap), end(oldmap),                         begin(newmap), end(newmap),                         std::inserter(diffmap, begin(diffmap)));      // output result     (auto& p : diffmap) {         std::cout << p.first << " " << p.second << std::endl;     } } 

output:

test1.txt 1 test3.txt 3 

these 2 entries not found in both maps.