1.----- is a C file function that can be used to indicate the current position of a stream while reading with a function like fread.Answer 1
ftell is the function the function that gives the current position. For example, if fread has read 100 bytes in a string, ftell will give an output of 100 indicating the current position.
2.Which is the function that can be used to test if a given character (input argument) is a hexadecimal digit?Answer 2
int isxdigit(int c) returns a non zero value if c is a hexadecimal digit.
3.Which is the data structure that is used in UNIX, that stores all essential information like access mode, type etc.?Answer 3
inode is the UNIX data structure that is responsible for storing file metadata.
4.Almost all UNIX operating systems are POSIX compliant. POSIX, as you know, indicates a set of standards for OS vendors to follow which eases the use of cross platform applications on all Operating Systems following POSIX. What is the expansion for POSIX ?Answer 4
POSIX stands for "Portable Operating System Interface".