C++ – How to utilise all the cores for nmake

c++eclipsemulticorenmakeqt

I just got a new quad core computer and noticed that nmake is only using 1 process.

I used to use make which had the switch -j4 for launching 4 processes. What is the nmake equivalent?

[edit]
Based on the information below I have been able to add a command to my qmake project file:

QMAKE_CXXFLAGS += /MP

Which effectively did it for me. Many thanks.

Best Solution

Another generic, non-Qt-related way to tell nmake to use all the cores is to set environmental variable CL to /MP:

set CL=/MP
nmake

will use all the CPU cores.

Related Solutions

C++ – What are the rules for calling the base class constructor

Base class constructors are automatically called for you if they have no argument. If you want to call a superclass constructor with an argument, you must use the subclass's constructor initialization list. Unlike Java, C++ supports multiple inheritance (for better or worse), so the base class must be referred to by name, rather than "super()".

class SuperClass
{
    public:

        SuperClass(int foo)
        {
            // do something with foo
        }
};

class SubClass : public SuperClass
{
    public:

        SubClass(int foo, int bar)
        : SuperClass(foo)    // Call the superclass constructor in the subclass' initialization list.
        {
            // do something with bar
        }
};

More info on the constructor's initialization list here and here.

C++ – Programmatically find the number of cores on a machine

C++11

#include <thread>

//may return 0 when not able to detect
const auto processor_count = std::thread::hardware_concurrency();

Reference: std::thread::hardware_concurrency

In C++ prior to C++11, there's no portable way. Instead, you'll need to use one or more of the following methods (guarded by appropriate #ifdef lines):

Win32

SYSTEM_INFO sysinfo;
GetSystemInfo(&sysinfo);
int numCPU = sysinfo.dwNumberOfProcessors;

Linux, Solaris, AIX and Mac OS X >=10.4 (i.e. Tiger onwards)
```
int numCPU = sysconf(_SC_NPROCESSORS_ONLN);
```

FreeBSD, MacOS X, NetBSD, OpenBSD, etc.

int mib[4];
int numCPU;
std::size_t len = sizeof(numCPU); 

/* set the mib for hw.ncpu */
mib[0] = CTL_HW;
mib[1] = HW_AVAILCPU;  // alternatively, try HW_NCPU;

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

if (numCPU < 1) 
{
    mib[1] = HW_NCPU;
    sysctl(mib, 2, &numCPU, &len, NULL, 0);
    if (numCPU < 1)
        numCPU = 1;
}

HPUX

int numCPU = mpctl(MPC_GETNUMSPUS, NULL, NULL);

IRIX
```
int numCPU = sysconf(_SC_NPROC_ONLN);
```

Objective-C (Mac OS X >=10.5 or iOS)

NSUInteger a = [[NSProcessInfo processInfo] processorCount];
NSUInteger b = [[NSProcessInfo processInfo] activeProcessorCount];