![]() You may hear that string operations are very cheap, unlikely to be a bottleneck and so forth… That might be so…īut I submit to you that the omnipresence of variable-length strings as a universal default can make us blind to very sweet optimization opportunities.Cp -R -f $lib Stringscan.app/Contents/libĭitto -rsrc -arch x86_64 Stringscan.app build/Stringscan.appįind build/Stringscan.app -type f -name "*. To summarize: Variable-length strings are a convenient abstraction. So, in fact, fixed-length strings could be nearly three times faster with enough work. For example, to keep the comparison “fair”, I sorted pointers to strings… but my padded C strings fit in a machine word and do not require a pointer. So for this experiment, replacing variable-length strings by fixed-length strings more than double the performance! And my code isn’t even optimized. How long does it take, in CPU cycles per string, to sort a short array of strings (1024 strings)? string type Instead of using variable-length strings, I can “pad” my strings so that they have a fixed length (8 characters), adding null characters as needed. In C++, they have standard strings ( std::string), with significant overhead: on my system, a single std::string uses 32 bytes, not counting the string content itself. In C, we use null-terminated characters, so the actual length is between 2 and 5. Such strings have length ranging between 1 and 4 characters. To examine this idea, I have created lists of strings made simply of the numbers (as strings) from 0 to 1024. However, maybe processors have gotten so smart, and string operations so optimized, that there is no clear performance benefits to fixed-length strings in today’s software.Įven today, it is often possible to accelerate software by replacing variable-length strings by fixed-length ones, when you know ahead of time that all your strings are going to be reasonably short. For example, if I were to store “tweets” (from Twitter) in memory, using a flat 140 characters per tweet, I would be able to support fast direct access without having to go through pointers. If the result field is not an array, the SCAN operation will locate only the first occurrence of the compare string. Yet fixed-length strings have clear engineering benefits. The SCAN begins at the leftmost character of factor 2 (as specified by the start location) and continues character by character, from left to right, comparing the characters in factor 2 to those in factor 1. All the recent programming languages I know ignore the concept of fixed-length strings. It seems that people today never worry about variable-length strings. When setting up a requisition, a hiring manager can split code it to an unlimited number of costing. Flat files with fixed-length lines and fixed-length records were common in the old days. Most relational databases support fixed-length strings. The Pascal programming language supported fixed-length strings. “Old” software often shied away from variable-length strings. For example, my name “Daniel” uses six characters whereas my neighbor’s name (“Philippe”) uses 8 characters. ![]() Much of our software deals with variable-length strings.
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