Build error

I was building my project and these are the errors that occured:-

server.c:-

#include"../Comman/headers.h"
  2 #include"../Comman/dataStruct.h"
  3 #include"declerations.h"
  4
  5 int main()
  6 {
  7     int ret;
  8     pthread_t thid;
  9     Infra *infra;
 10 #ifdef DEBUG
 11        printf("%s: Begin.\n", __func__);
 12 #endif
 13         init();
 14       infra = (*fptr[1])(0);     // creatInfra();
 15
 16       while(1)
 17       {
 18         sem_wait(&infra->tsem);
 19        ret = pthread_create(&thid, NULL, fptr[2], 0);
 20        if(ret == -1)
 21         {
 22             perror("pthread_create");
 23             (*fptr[0])((void*)"failure");     //  exitProgram();
 24         }
 25       }
 26
 27 #ifdef DEBUG
 28        printf("%s: End.\n", __func__);
 29 #endif
 30         return 0;
 31 }

These are the errors encountered:-

usr/bin/ld: server.o: in function `main':
server.c:(.text+0x44): undefined reference to `sem_wait'
/usr/bin/ld: server.c:(.text+0x61): undefined reference to `pthread_create'
/usr/bin/ld: creatInfra.o: in function `creatInfra':
creatInfra.c:(.text+0x2b4): undefined reference to `sem_init'
collect2: error: ld returned 1 exit status