How to get the number of CPUs in Linux using C?

In Linux systems, obtaining the CPU count using C can be achieved through several methods, with one common approach being the use of the sysconf function.

The sysconf function can query runtime system configuration information, such as the number of CPUs.

Below is an example of using the sysconf function to retrieve the CPU count.

c
#include <stdio.h>
#include <unistd.h>

int main() {
    // Use sysconf to query CPU count
    long num_cpus = sysconf(_SC_NPROCESSORS_ONLN);

    // Output CPU count
    printf("Number of CPUs available: %ld\n", num_cpus);

    return 0;
}

In this code snippet, the parameter _SC_NPROCESSORS_ONLN of the sysconf function represents the query for the number of currently online processors. This value indicates the number of available processor cores in the system, which is dynamic and reflects scenarios where certain cores are disabled.

The advantage of this method is its simplicity and ease of implementation, as well as its compatibility across various Unix-like systems, including Linux. Additionally, the return value of the sysconf function is a long integer (long), ensuring accurate representation even on systems with a large number of cores.

This method is highly useful when developing applications such as system monitoring tools or parallel computing programs that require behavior adjustments based on the CPU count. For example, a parallel task processing program can determine the number of threads or processes to launch based on the system's CPU count to maximize resource utilization efficiency.