Saturday, January 28, 2012

Some inportant question of file handeling in c program

Q1). What are the two forms of #include directive?
2.#include <>
the first form is used to search the directory that contains the source file. If the search fails in the home directory it searches the implementation defined locations. In the second form ,the preprocessor searches the file only in the implementation defined locations.

Q2). How would you use the functions fseek(), freed(), fwrite() and ftell()?
fseek(f,1,i) Move the pointer for file f a distance 1 byte from location i.
fread(s,i1,i2,f) Enter i2 data items, each of size i1 bytes, from file f to string s.
fwrite(s,i1,i2,f) send i2 data items, each of size i1 bytes from string s to file f.
ftell(f) Return the current pointer position within file f.
The data type returned for functions fread, fseek and fwrite is int and ftell is long int.

Q3). What is a file?
Ans: A file is a region of storage in hard disks or in auxiliary storage devices. It contains bytes of
information .It is not a data type.

Q4.) IMP>what are the types of file?
Ans: Files are of two types
1-high level files (stream oriented files) :These files are accessed using library functions
2-low level files(system oriented files) :These files are accessed using system calls

Q5). IMP>what is a stream?
Ans: A stream is a source of data or destination of data that may be associated with a disk or other
I/O device. The source stream provides data to a program and it is known as input stream. The destination stream receives the output from the program and is known as output stream.

Q6). What is meant by file opening?
Ans: The action of connecting a program to a file is called opening of a file. This requires creating
an I/O stream before reading or writing the data.

Q7). What is FILE?
Ans: FILE is a predefined data type. It is defined in stdio.h file.

Q8) What is a stream?
A stream is a continuous series of bytes that flow into or out of your program. Input and output from devices such as the mouse, keyboard, disk, screen, modem, and printer are all handled with streams. In C, all streams appear as files - not physical disk files necessarily, but rather logical files that refer to an input/output source. The C language provides five "standard" streams that are always available to your program. These streams do not have to be opened or closed. These are the five standard streams:


Standard Input
Standard Output
Standard Error
Standard Printer
LPT1: port
Standard Auxiliary
COM1: port
Note that the stdprn and stdaux streams are not always defined. This is because LPT1: and COM1: have no meaning under certain operating systems. However, stdin, stdout, and stderr are always defined. Also, note that the stdin stream does not have to come from the keyboard; it can come from a disk file or some other device through what is called redirection. In the same manner, the stdout stream does not have to appear on-screen; it too can be redirected to a disk file or some other device. See the next FAQ for an explanation of redirection.

 Q9) 3. How do you redirect a standard stream?

Most operating systems, including DOS, provide a means to redirect program input and output to and from different devices. This means that rather than your program output (stdout) going to the screen, it can be redirected to a file or printer port. Similarly, your program's input (stdin) can come from a file rather than the keyboard. In DOS, this task is accomplished using the redirection characters, < and >. For example, if you wanted a program named PRINTIT.EXE to receive its input (stdin) from a file named STRINGS.TXT, you would enter the following command at the DOS prompt:
Notice that the name of the executable file always comes first. The less-than sign (<) tells DOS to take the strings contained in STRINGS.TXT and use them as input for the PRINTIT program.
Redirection of standard streams does not always have to occur at the operating system. You can redirect a standard stream from within your program by using the standard C library function named freopen(). For example, if you wanted to redirect the stdout standard stream within your program to a file named OUTPUT.TXT, you would implement the freopen() function as shown here:

freopen("output.txt", "w", stdout);

Now, every output statement (printf(), puts(), putch(), and so on) in your program will appear in the file OUTPUT.TXT.

Q10) What is the difference between text and binary modes?
Streams can be classified into two types: text streams and binary streams. Text streams are interpreted, with a maximum length of 255 characters. With text streams, carriage return/line feed combinations are translated to the newline n character and vice versa. Binary streams are uninterrupted and are treated one byte at a time with no translation of characters. Typically, a text stream would be used for reading and writing standard text files, printing output to the screen or printer, or receiving input from the keyboard.

A binary text stream would typically be used for reading and writing binary files such as graphics or word processing documents, reading mouse input, or reading and writing to the modem.

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