In an earlier blog post, I reported that the memory usage of a small byte array in Java (e.g., an array containing 4 bytes) was about 24 bytes. In other words: allocating small blocks of memory has substantial overhead.
What happens in C++?
To find out, I can try to allocate one million 4-byte arrays and look at the total memory usage of the process. Of course, the memory usage of the process will include some overhead unrelated to the 4-byte arrays, but we expect that such overhead will be relatively small.
From my benchmark, I get the following results…
| system | memory usage (in bytes) |
|---|---|
| GCC 8, Linux x86 | 32 bytes |
| LLVM 14, Apple aarch64 | 16 bytes |
The results will vary depending on the configuration of your system.
The lesson is that allocating four bytes (new char[4] or malloc(4)) does not use four bytes of memory… it will generally use much more.
