How Can I Portably Determine a Machine's Core Count in C ?

Platform-Independent Determination of Machine's Core Count

Determining the number of cores on a machine can be essential for optimizing software performance. However, finding a platform-independent solution for this task can be challenging.

C 11 Solution

Fortunately, C 11 has introduced a platform-agnostic method for identifying core count:

#include <thread>

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

This method returns the logical number of cores, as reported by the underlying hardware and operating system.

Pre-C 11 Solutions

For C versions prior to C 11, there is no portable way to determine core count. Instead, platform-specific approaches must be used:

Windows

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

Unix-like Systems

int numCPU = sysconf(_SC_NPROCESSORS_ONLN);

macOS (Prior to 10.5)

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;

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

Objective-C (macOS 10.5 or Later)

NSUInteger a = [[NSProcessInfo processInfo] processorCount];

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