Counting the number of CPUs
Because each cpu has a directory whose name is
cpu followed by at least one digit, the following
C program counts the numbers of
CPUs in a system:
#include <stdio.h>
#include <dirent.h>
#include <sys/stat.h>
#include <string.h>
#include <ctype.h>
#define MAX_PF_NAME 1024
#define SYSFS_DEVCPU "/sys/devices/system/cpu"
int nof_cpus() {
DIR *dir;
struct dirent *drd;
struct stat cpu_dir_stat;
char cpu_dir_name[MAX_PF_NAME];
int cpu_count = 0;
if ((dir = opendir(SYSFS_DEVCPU)) == NULL)
return 0;
while ((drd = readdir(dir)) != NULL) {
if (!strncmp(drd->d_name, "cpu", 3) && isdigit(drd->d_name[3])) {
snprintf(cpu_dir_name, sizeof(cpu_dir_name), "%s/%s", SYSFS_DEVCPU, drd->d_name);
cpu_dir_name[sizeof(cpu_dir_name) - 1] = '\0';
if (stat(cpu_dir_name, &cpu_dir_stat) < 0)
continue;
if (S_ISDIR(cpu_dir_stat.st_mode)) {
cpu_count++;
}
}
}
closedir(dir);
return cpu_count;
}
int main() {
printf("nof_cpus = %d\n", nof_cpus());
}