How Can I Programmatically Determine the Number of Cores on a Machine?

Determining the Number of Cores on a Machine Programmatically

In various computing scenarios, understanding the number of cores available on a machine is crucial. C/C does not offer a platform-independent solution for this task. However, there are platform-specific approaches that can provide this information.

C 11 (Platform-Independent)

C 11 introduces the std::thread::hardware_concurrency() function, which provides a portable method to obtain the number of cores.

#include <thread>

const auto processor_count = std::thread::hardware_concurrency();

Pre-C 11 (Platform-Specific)

In C prior to C 11, specific methods must be used depending on the platform:

Win32

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

Linux, Solaris, AIX, Mac OS X >=10.4

int numCPU = sysconf(_SC_NPROCESSORS_ONLN);

FreeBSD, MacOS X, NetBSD, OpenBSD

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);

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];

By utilizing these platform-specific methods or the C 11 platform-independent approach, you can programmatically determine the number of cores available on a machine, enabling you to optimize resource utilization and achieve better performance in your applications.

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