We are going to use simple shell commands to adjust the parameters of CPU frequency on a Raspberry PI box: 

1. Log in to a Raspberry Pi or another nonvirtualized Linux system.
2. Switch to the root account:

$ sudo bash
#

3. Get the current frequency of all CPU cores available in the system:

# cat /sys/devices/system/cpu/*/cpufreq/scaling_cur_freq

4. Get all of the frequencies supported by the CPU:

# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies

5. Get the available CPU-frequency governors:

# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors

6. Now let's check which frequency governor is currently in use:

# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor 

7. Adjust the minimum frequency of the CPU to the highest supported:

# echo 1200000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq

8. Display the current frequencies again to understand the effect:

# cat /sys/devices/system/cpu/*/cpufreq/scaling_cur_freq

9. Adjust the minimum frequency to the lowest supported:

# echo 600000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_fre

10. Now let's check how the CPU frequency depends on the governor in use. Select a performance governor and get the current frequency:

# echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
# cat /sys/devices/system/cpu/*/cpufreq/scaling_cur_freq

11. Select the powersave governor and observe the result:

# echo powersave > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
# cat /sys/devices/system/cpu/*/cpufreq/scaling_cur_freq

You can use a regular file API to implement the same logic in C++.