Windows-API-examples/system/cpu_speed.c

#include <windows.h>
#include <wchar.h>

int wmain(void) {

    DWORD BufSize = MAX_PATH;
    DWORD mhz = MAX_PATH;
    HKEY key;

    long r = RegOpenKeyExW(HKEY_LOCAL_MACHINE,
        L"HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0", 0, KEY_READ,	&key);

    if (r != ERROR_SUCCESS) {

        wprintf(L"RegOpenKeyExW() failed %ld", GetLastError());
    	return 1;
    }

    r = RegQueryValueExW(key, L"~MHz", NULL, NULL, (LPBYTE) &mhz, &BufSize);

    if (r != ERROR_SUCCESS) {

        wprintf(L"RegQueryValueExW() failed %ld", GetLastError());
        return 1;
    }

    wprintf(L"CPU speed: %lu MHz\n", mhz);

    r = RegCloseKey(key);

    if (r != ERROR_SUCCESS) {

        wprintf(L"Failed to close registry handle %ld", GetLastError());
        return 1;
    }
    
    return 0;
}