Ulimit limit memory usage by program

Question

I want to limit the memory usage of the program. I searched the Internet and found that ulimit -v can be used for this. After using this command, I could see the restriction with ulimit -a. However, my program still uses the same amount of memory. I checked the memory usage with the top command while the program was running. I have not seen the restriction take place. Something is wrong? I am using CentOS Linux version 7.1.1503 (Core).