Memory mapping is not beneficial: methodĪs usual, my benchmark code is available for inspection. To support my claim, I created a little program that reads arrays of integers from a file, and does some minor computations on them. For this kind of access pattern, I have never found memory mapping to be useful. However, in my experience, it is also less stable: you are unlikely to cause a bus error with fread or ifstream, but the slightest mistake with memory mapping and your program can crash.įor my work, a lot of the IO is based on sequential access. It has the reputation to be very fast because the data on disk can be mapped directly to memory without any undue copying. Instead of reading blocks of data, you map the content of the file to a pointer and the operating system is responsible with filling in the data. It is very similar to fread, but with a more object-oriented flavor.
#Difference between istream and ifstream software
Buffers usually makes software faster because copying data in memory is much faster than reading it from disk. That is, they may cause the data to be copied needlessly. On the other hand, they introduce an intermediate step between the disk and you data. On the one hand, they reduce the number of disk accesses. Unlike the read function, you can set a buffer size. The standard C library also offers a higher level fread function.The standard C library offers a low-level read function.If you program in C/C++, you have many options to read files: Bernard B on Escaping strings faster with AVX-512.Daniel Lemire on Escaping strings faster with AVX-512.
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