foo.shell

sysctl $ cat Dockerfile                                                                                                                                                                    
from ubuntu:bionic

RUN apt update > /dev/null 2>&1
RUN apt install -y g++ vim > /dev/null 2>&1
COPY machineInfo.cpp .
RUN echo | g++ -dM -E - | grep linux
RUN g++ machineInfo.cpp
sysctl $ cat machineInfo.cpp                                                                                                                                                               
#include <sys/sysctl.h>
#include <linux/sysctl.h>
#include <cstdio>

#define ARRAY_SIZE(a) (sizeof (a) / sizeof ((a)[0]))

int num_procs(void) {

    int numCPU = 0;
    int nprocs;
    size_t len = sizeof(nprocs);
    static int mib[2] = { CTL_HW, HW_NCPU };

    /* get the number of CPUs from the system */
    sysctl(mib, 2, &numCPU, &len, NULL, 0);

    if( numCPU < 1 )
        {
        mib[1] = HW_NCPU;

        if (sysctl (mib, ARRAY_SIZE(mib), &nprocs, &len, NULL, 0) == 0 && len == sizeof (nprocs) && 0 < nprocs)
            numCPU = nprocs;

        if( numCPU < 1 )
            numCPU = 1;
        }
    return numCPU;

}
sysctl $ docker build . --no-cache                                                                                                                                                         
Sending build context to Docker daemon  3.584kB
Step 1/6 : from ubuntu:bionic
 ---> 47b19964fb50
Step 2/6 : RUN apt update > /dev/null 2>&1
 ---> Running in d28dfd3539fc
Removing intermediate container d28dfd3539fc
 ---> 49cb6d48c991
Step 3/6 : RUN apt install -y g++ vim > /dev/null 2>&1
 ---> Running in beb45f9a69b7
Removing intermediate container beb45f9a69b7
 ---> 1d6014480000
Step 4/6 : COPY machineInfo.cpp .
 ---> 8dc7bc82b7f8
Step 5/6 : RUN echo | g++ -dM -E - | grep linux
 ---> Running in 6b391c4ee975
#define __linux 1
#define __linux__ 1
#define __gnu_linux__ 1
#define linux 1
Removing intermediate container 6b391c4ee975
 ---> e1a2afd74092
Step 6/6 : RUN g++ machineInfo.cpp
 ---> Running in 34016ec497a3
machineInfo.cpp: In function 'int num_procs()':
machineInfo.cpp:12:27: error: 'CTL_HW' was not declared in this scope
     static int mib[2] = { CTL_HW, HW_NCPU };
                           ^~~~~~
machineInfo.cpp:12:27: note: suggested alternative: 'CTL_PM'
     static int mib[2] = { CTL_HW, HW_NCPU };
                           ^~~~~~
                           CTL_PM
machineInfo.cpp:12:35: error: 'HW_NCPU' was not declared in this scope
     static int mib[2] = { CTL_HW, HW_NCPU };
                                   ^~~~~~~
The command '/bin/sh -c g++ machineInfo.cpp' returned a non-zero code: 1