C error undefined reference to clock gettime and clock settime

Question

I am pretty new to Ubuntu  but I can t seem to get this to work   It works fine on my school computers and I don t know what I am not doing   I have checked usr include and time h is there just fine   Here is the code    include  lt iostream gt   include  lt time h gt  using namespace std   int main         timespec time1  time2      int temp      clock gettime CLOCK PROCESS CPUTIME ID   amp time1         do stuff here     clock gettime CLOCK PROCESS CPUTIME ID   amp time2       return 0      I am using CodeBlocks as my IDE to build and run as well  Any help would be great  thank you

User · Answer

I encountered the same error   My linker command did have the rt library included -lrt which is correct and it was working for a while  After re-installing Kubuntu it stopped working   A separate forum thread suggested the -lrt needed to come after the project object files  Moving the -lrt to the end of the command fixed this problem for me although I don t know the details of why

User · Answer

example   c   -Wall filefork cpp -lrt -O2   For gcc version 4 6 1  -lrt must be after filefork cpp otherwise you get a link error    Some older gcc version doesn t care about the position

User · Answer

Add -lrt to the end of g   command line  This links in the librt so  Real Time  shared library

User · Answer

Since glibc version 2 17  the library linking -lrt is no longer required    The clock   are now part of the main C library  You can see the change history of glibc 2 17 where this change was done explains the reason for this change      The  clock    suite of functions  declared in  lt time h gt   is now available    directly in the main C library   Previously it was necessary to link with    -lrt to use these functions   This change has the effect that a    single-threaded program that uses a function such as  clock gettime   and    is not linked with -lrt  will no longer implicitly load the pthreads    library at runtime and so will not suffer the overheads associated with    multi-thread support in other code such as the C   runtime library    If you decide to upgrade glibc  then you can check the compatibility tracker of glibc if you are concerned whether there would be any issues using the newer glibc      To check the glibc version installed on the system  run the command   ldd --version    Of course  if you are using old glibc   lt 2 17  then you will still need -lrt

[c++] C++ error: undefined reference to 'clock_gettime' and 'clock_settime'

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