Undefined reference to clock_gettime() in Linux using ICC

Question

I am trying to get the code (see far below) working on Ubuntu. The code uses clock_gettime(). I think I have successfully linked to librt.a:

**** Build of configuration Debug for project test ****

make -k all 
Building file: ../src/test.cpp
Invoking: Intel Intel(R) 64 C++ Compiler 
icpc -g -I/usr/include/boost -std=c++0x -MMD -MP -MF"src/test.d" -MT"src/test.d" -c -o "src/test.o" "../src/test.cpp"
Finished building: ../src/test.cpp

Building target: test
Invoking: Intel Intel(R) 64 C++ Linker
icpc  -l  /usr/lib/x86_64-linux-gnu/librt.a  -o "test"  ./src/test.o   
icpc: command line warning #10155: ignoring option '-l'; argument required
./src/test.o: In function `main':
/home/p/workspace/test/Debug/../src/test.cpp:12: undefined reference to `clock_gettime'
/home/p/workspace/test/Debug/../src/test.cpp:15: undefined reference to `clock_gettime'
make: *** [test] Error 1
make: Target `all' not remade because of errors.

**** Build Finished ****

However, I still get the error about undefined reference to clock_gettime. This is my code:

#include <iostream>
#include <time.h>
using namespace std;

timespec diff(timespec start, timespec end);

int main()
{
    timespec time1, time2;
    int temp;
    clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time1);
    for (int i = 0; i< 242000000; i++)
        temp+=temp;
    clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time2);
    cout<<diff(time1,time2).tv_sec<<":"<<diff(time1,time2).tv_nsec<<endl;
    return 0;
}

timespec diff(timespec start, timespec end)
{
    timespec temp;
    if ((end.tv_nsec-start.tv_nsec)<0) {
        temp.tv_sec = end.tv_sec-start.tv_sec-1;
        temp.tv_nsec = 1000000000+end.tv_nsec-start.tv_nsec;
    } else {
        temp.tv_sec = end.tv_sec-start.tv_sec;
        temp.tv_nsec = end.tv_nsec-start.tv_nsec;
    }
    return temp;
}

can someone please help?

@chrisaycock on ICC there is -L for a directory and -l for the library file. You reckon I should try -l librt.a and -L /usr/lib/x86_64-linux-gnu/ ? — user997112, Jun 15 '13 at 23:15

score 9 · Accepted Answer · answered Jun 15 '13 at 23:14

9

It looks like you haven't linked librt.a at all since the linker is ignoring -l. Perhaps you were supposed to use -lrt and optionally give the path via -L.

icpc  -lrt -L/usr/lib/x86_64-linux-gnu -o "test"  ./src/test.o

Notice I have no spaces between the -l and its parameter. I also have listed "librt.a" as merely rt; the linker will add the rest on its own.

answered Jun 15 '13 at 23:14

chrisaycock

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Thank you ever so much! I did not realise you had to remove the "lib" part of the library name!! – user997112 Jun 15 '13 at 23:21

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

Besides adding -lrt to the linker flags, it's strongly recommended to add -Wl, -no-as-needed to the linker flags as well. Ref from man ld:

--as-needed

--no-as-needed

This option affects ELF DT_NEEDED tags for dynamic libraries mentioned on the command line after the --as-needed option. Normally the linker will add a DT_NEEDED tag for each dynamic library mentioned on the command line, regardless of whether the library is actually needed or not. --as-needed causes a DT_NEEDED tag to only be emitted for a library that satisfies an undefined symbol reference from a regular object file or, if the library is not found in the DT_NEEDED lists of ther libraries linked up to that point, an undefined symbol reference from another dynamic library. --no-as-needed restores the default behaviour.

Undefined reference to clock_gettime() in Linux using ICC

2 Answers2

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