c++ - Cout gives no output after declaring an std::string variable -

i've written simple program returning hostname of ip address passed argument. program uses 2 functions: getaddrinfo() , getnameinfo(). i'm using linux mint, netbeans ide , g++ compiler. output alright, there no errors, when declare an

std::string str; 

then cout gives no output, nothing printed on screen. when comment out std::string declaration or remove it, statement

std::cout << "hostname: " << hostname << std::endl; 

prints returned hostnames successfully.

what may cause of such strange error?

#include <netdb.h> #include <netinet/in.h> #include <sys/socket.h> #include <iostream> #include <string>  int main() {     struct addrinfo* result;     struct addrinfo* res;     int error;     const char* host;     // when comment out line, cout prints hostnames succesfully.     std::string str;      error = getaddrinfo("127.0.0.1", null, null, &result);     res = result;      while (res != null)     {         char* hostname;         error = getnameinfo(res->ai_addr, res->ai_addrlen, hostname, 1025, null, 0, 0);         std::cout << "hostname: " << hostname << std::endl;         res = res->ai_next;     }      freeaddrinfo(result);     // when declare std::string str variable, cout doesn't either print     std::cout << "test" << std::endl;      return 0; } 

   arguments host , serv pointers caller-    allocated buffers (of size hostlen , servlen respectively)    getnameinfo() places null-terminated strings containing host ,    service names respectively. 

http://man7.org/linux/man-pages/man3/getnameinfo.3.html

your pointers must allocated. fact commenting out line changes coincidence or strange side effect of optimization.