Convert string to int c8/7/2023 ![]() ![]() But what about just extracting the first number from a string? This wouldn’t then require the starting position of the next conversion to be set, or sub-strings to be extracted. These timings were to extract numbers from a single string in which they were separated by multiple spaces. A simpler use case: extracting the first number from a string So the new conversion std::from_chars() certainly fulfils its promise re performance and is also easy to use. The first thing that hit me when I initially saw these figures was how slow stream extraction is compared to the other methods – and the second was how fast the new std::from_chars() function is! For coliru it is twice as fast as the next fastest ( strtoul()) and for the laptop/Lenovo about three times as fast (although for 圆4 the ratio is slightly less). For all except coliru, the compiler used is MS VS2017 15.7.4 with all optimizations enabled and optimized for speed (x86 unless specified). Laptop2 is Windows 7 64-bit, 4 GB memory, Intel i5 processor 2.6 GHZ and a SSD. Lenovo is Windows 10 64-bit, 8 GB memory, Intel i5 processor 2.6 GHZ and a hard disk. Laptop1 is Windows 7 64-bit, 16 GB memory, Intel i7 processor 2.6 GHZ and a hard disk. Note that all timings are in milli-seconds. The table below gives details of the performance results obtained, for extracting numbers from a single string in which they are separated by multiple spaces: The test code can be found in this coliru. In this Part 2, we will examine the performance of these various conversion methods and provide suggestions for performance improvements. We discussed their pros and cons and gave examples of their usage in the context of obtaining a vector of unsigned integers from a single string in which numbers were separated by multiple spaces. In Part 1 we looked at the different options available and in particular the new std::from_chars() conversion function available in C++17. This is Part 2 in our series about conversion from characters to integers. Interested in writing on Fluent C++ too? Check out the guest posting area. In this post, jft presents the performance analyses he conducted to find out which method is fastest to extract numbers from a string. Today’s guest post is written by guest author jft, as a sequel to his previous article How to Convert a String to an int in C++. ![]()
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