c++ - Vectors of lock_guards -

i'm working multithreaded code (working concurrent data structures), , part of requires lock set of mutexes. implementation utilizing vector of lock_guards, since don't know how many mutexes i'm going need lock, , may run exception conditions force me unlock of mutexes , restart. hence reason vector.

the code i'm trying use boils down this:

#include <mutex> #include <vector>   using namespace std;  int main( int argc, char** argv ) {     vector<recursive_mutex> vec(10);      vector<lock_guard<recursive_mutex>> lgv;     for( auto = vec.begin(); != vec.end(); ++it ) {         lgv.emplace_back( *it );     }      return 0; } 

when try compile (g++ 5.3.1 using --std=c++11), following error (somewhat distilled):

in file included foo.cpp:1:0: /usr/include/c++/5.3.1/mutex:385:7: note: declared here    lock_guard(const lock_guard&) = delete; 

based upon understanding of emplace_back, library should not attempting use copy constructor lock_guard -- should performing construct-in-place. understanding should happening properly, or understanding flawed?

fyi, have attempted use unique_lock , compile fine. however, i'm curious (apparent) discrepancy.

i assume, question reflects attemtpt use unique_lock, op saying works. same example lock_guard not work, since std::vector::emplace_back requires type both moveinsertable , emplaceconstructible, , std::lock_guard not suit.