I have a file of size 1GB. I want to find out how many times the word "sosowhat" is found in the file. I've written a code using fgetc() which reads one character at a time from the file which is way too slower when it comes for a file of size 1GB. So I made a buffer of size 1000(using mmalloc) to hold 1000 words at a time from the file and I used the strstr() function to count the occurrence of the word "sosowhat". The logic is fine. But the problem is that if the part "so" of "sosowhat" is located at the end of the buffer and the "sowhat" part in the new buffer, the word will not be counted. So I used two buffers old_buffer and current_buffer. At the beginning of each buffer I want to check from the last few characters of old buffer. Is this possible? How can I go back to the old buffer? Is it possible without memmove()? As a beginner, I will be more than happy for your help.
Is it possible to count the frequency of a word in a file precisely using two buffers in C?
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2 Answers
Yes, it can be done. There are more possible approaches to this.
The first one, which is the cleanest, is to keep a second buffer, as suggested, of the length of the searched word, where you keep the last chunk of the old buffer. (It needs to be exactly the length of the searched word because you store wordLength - 1 characters + NULL terminator). Then the quickest way is to append to this stored chunk from the old buffer the first wordLen - 1 characters from the new buffer and search your word here. Then continue with your search normally. - Of course you can create a buffer which can hold both chunks (the last bytes from the old buffer and the first bytes from the new one).
Another approach (which I don't recommend, but can turn out to be a bit easier in terms of code) would be to fseek wordLen - 1 bytes backwards in the read file. This will "move" the chunk stored in previous approach to the next buffer. This is a bit dirtier as you will read some of the contents of the file twice. Although that's not something noticeable in terms of performance, I again recommend against it and use something like the first described approach.
use the same algorithm as per fgetc only read from the buffers you created. It will be same efficient as strstr iterates thorough the string char by char as well.
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