Given a huge file having dynamic data, write a program to read last n lines from the file at any point without reading the entire file. The problem is similar to tail command in linux which displays the last few lines of a file. It is mostly used for viewing log file updates as these updates are appended to the log files.
Source : Microsoft Interview
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The problem mainly focuses on below things –
1. The program should not read entire file.
2. The program should handle incoming dynamic data and returns last n lines at any point.
3. The program should not close input stream before reading last n lines.
Below is its C++ implementation
Some points to Note –
1. This code won’t work on online compiler as it requires file creation permissions. When run local machine, it produces sample input file “input.txt” and dynamically write data to it 10 times and calls tail() function every time.
2. We should avoid using fseek() and ftell() for huge files(in GBs) as they operate on file positions of type long int. Use _fseeki64(), _ftelli64() instead.
3. unsigned long has max allowed value of 232 – 1 (Assuming that unsigned long takes 4 bytes). It can be used for files size of less than 4 GB file.
4. unsigned long long has max allowed value of 264 – 1 (Assuming that unsigned long long takes 8 bytes). It can be used for files size over 4 GB.
This article is contributed by Aditya Goel. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above