How to measure sequential memory read speed in C/C++

Question

The problem does not take CPU cache into consideration. That is, let the cache do its job (let cpu cache improve the performance).
My idea is to allocate a big enough chunk of memory (so that not all of it fit into cache) and treat them as one data type(like int) and do addition to avoid the compiler completely optimize away the code to read the memory. The problem is does the data type affect the measurement? Or is there a more general way of doing it?
EDIT: Might be a bit mis-leading before. An example is AIDA64's memory and cache benchmark, which is able to measure the memory read/write speed as well as latency. I want to know a general idea of how it is done.

Cort Ammon · Answer

Microbenchmarks like this are not easy in C/C++.  The amount of time something takes in C++ is not a specified aspect of the language.  Indeed, for every use case except this one, faster is better, so compilers are encouraged to do smart things.
The trick to these is to write the benchmark, compile it, and then look at the assembly to see whether its doing clever tricks.  Or, at the very least, check to make sure that it makes sense (accessing more memory = more time).
Compilers are getting smart.  Addition is not always enough.  More than once I've had Visual Studio realize what I was doing to construct the microbenchmark and compile it all away.
At the moment, I am having good luck using the argc argument passed into main as a seed, and using a cryptographic hash like SHA1 or MD-5 to fill the data.  This tends to be enough to trick the compiler into actually writing all of the reads.  But verify your results.  There's no guarantee that a new compiler doesn't get even smarter.

How to measure sequential memory read speed in C/C++

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