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I was asked by an interviewer that how would I implement tail (yes, the one in linux shell). My answer was, first seek to the end of the file, then read characters one-by-one forward, if encounters a \n, means one line is down, blah blah blah. I assume my answer is correct.
Then I found this problem, which seek should I use to implement tail? I thought I can simply use seekg (C++ thing?), but I was told that I should use lseek (linux system call?).
So including fseek (ANSI C thing?), which one should I use to implement tail? And is there any big difference between them?
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seekg moves the file input pointer(position of reading frm file) while seekp moves file output pointer( position f writing to file).
seekg() and seekp() both are functions of File Handling in C++ and they are very important and useful feature of File Handling in C++. In File Handling of C++, we have two pointers one is get pointer and second is put pointer.
seekg() is a function in the iostream library that allows you to seek an arbitrary position in a file. It is included in the <fstream> header file and is defined for istream class. It is used in file handling to sets the position of the next character to be extracted from the input stream from a given file.
The tellp() function is used with output streams, and returns the current “put” position of the pointer in the stream. It has no parameters and return a value of the member type pos_type, which is an integer data type representing the current position of the put stream pointer.
Use seekg when using the C++ IOstreams library. seekp is no use here, since it sets the put pointer.
Use fseek when using the C stdio library. Use lseek when using low-level POSIX file descriptor I/O.
The difference between the various seek functions is just the kind of file/stream objects on which they operate. On Linux, seekg and fseek are probably implemented in terms of lseek.
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