Need assistance C++ compiler and linker error messages -

i've been working on program assignment college , i'm done got strange error,and can't find solution anywhere. 1 function program.so...it throws error on part of code. xor operator seems problem. have tried rename name of "nesto" variable in case same name of function no success. please help! ideas ? suggestions ?

error: no match call ‘(std::string {aka std::basic_string}) (int&)’

void* ukupno(void* naziv){     while(kraj!=1){         sem_wait(&s_suma);         for(int v=0;v<uk_buffer;v++)                  nesto^= buffer(v);          sem_post(&s_dohvati);            }     } 

here entire code :

#include <iostream> #include <fstream> #include <cstdlib> #include <string.h> #include <unistd.h> #include <sys/wait.h> #include <algorithm> #include <pthread.h>  #include <semaphore.h> #include <signal.h> #include <sys/wait.h>  using namespace std; bool zastavica=1,kraj; int uk_buffer,broj=0,nesto=0; string buffer;   sem_t s_dohvati; sem_t s_broji_rijeci; sem_t s_suma;   void otvori_dat(string naziv){     fstream dat;     cout<<"naziv   " << naziv << endl;     dat.open("naziv",ios::in);       }  void* dohvati(void* naziv){      fstream dat;     dat.open((char*)naziv,ios::in);     if(!dat){             cout<<"greska kod otvaranja datoteke !!! " << endl;             exit(-1);}     kraj = false;     while(!kraj){                 getline(dat,buffer);                 uk_buffer = buffer.length();                 if(dat.eof()) kraj = true;                  sem_post(&s_broji_rijeci);                 sem_post(&s_suma);      if(kraj) sem_wait(&s_dohvati),sem_wait(&s_dohvati);     }                                    dat.close();     }  void broji_txt(){              for(int i=0;i<uk_buffer;i++)                   if(isalnum(buffer[i])){                         broj++;                         while(isalnum(buffer[++i]));                         }                 }           void broji_html(){  (int i=1;i<uk_buffer;i++)                 if (buffer[i-1]=='<'&&buffer[i]!='/')                         broj++;                         }   void* broji_rijeci(void* naziv){     while(kraj!=1){         sem_wait(&s_broji_rijeci);             if(zastavica) broji_txt();             else broji_html();         sem_post(&s_dohvati);//postavljanje         }     }  void* ukupno(void* naziv){     int nesto=0;     while(kraj!=1){         sem_wait(&s_suma);         for(int v=0;v<uk_buffer;v++)                  nesto^= buffer(v);          sem_post(&s_dohvati);            }     }  void analiza(char* naziv){     pthread_t pt_dohvati, pt_broji_rijeci, pt_suma;      sem_init (&s_dohvati,0,0);     sem_init (&s_broji_rijeci,0,0);     sem_init (&s_suma,0,0);      pthread_create (&pt_dohvati,null,dohvati,(void*)naziv);     //zadnji parametar je ono što šaljem;     pthread_create (&pt_broji_rijeci,null,broji_rijeci,null);     pthread_create (&pt_suma, null, ukupno, null);      pthread_join(pt_dohvati,null);     pthread_join(pt_broji_rijeci,null);     pthread_join(pt_suma,null);     cout << "datoteka " << naziv << " ima " << broj << "rijeci/tagova, zastitna suma je: " <<(unsigned int)nesto; }   int main(int arg0 , char* arg1[]){     char* pom;     int br_arg = arg0-1;//po njemu se orijentiramo      for(int k=1; k<=br_arg;k++){         pom=strchr(arg1[k],'.');         if(strcmp(pom,".txt") == 0)             zastavica=1;         else if(strcmp(pom,".html") == 0)   zastavica=0;         else cout<< "datoteka " << arg1[k] << " nije podrzanog formata " <<  endl;         switch(fork()){                     case  0 : analiza(arg1[k]),exit(0);                     case -1 : cerr<< "pogreska pri stvaranju procesa" << endl;                     default : continue;                         }                                 }             for(int i=0; < br_arg ;i++)   wait (null);         return 0; } 

the error message telling there no way use function call syntax if you've got isn't function string. instead of buffer(v), meant buffer[v]. type of brackets used matters.