Explain about Various File Handling Functions in C?

In C files are handled with the library functions. The following are few functions that are used with text files as well as binary files. 1. fopen ( ) 2. fclose ( ) 3. fclose all ( ) 4. feof ( ) 5. ferror ( )

1. Defining and opening a files: If we want to store data in a file in the secondary memory, we must specify certain things about the file, to the opening system. They include  : 1. File name              2. Data structure                   3. Purpose File name is a string of characters that make up a valid filename. It may contain two parts, a primary name and as optical period with the extension. Ex: Input.data, student.C Data structure of a file is defined as FILE in the library of standard I/O function definitions. Therefore all files should be declared as type FILE before they are used. When we open a file, we must specify what we want to do with the file. For ex: we may write data to the file or read the already existing data. General format for declaring and opening a file. File fp: fp=fopen ( “file name”, “mode”); The first statement declares the variable fp as a pointer to the data type FILE. The second statement opens the file named filename and assigns an identifier to the FILE type pointer fp. This pointer, which contains all the info about the file. The second statement also specifies the purpose of opening this file. The mode does this job. mode can be one of the following. r Open the file for reading only w Open the file for writing  only a Open the file of appending ( or adding) data to it r+ The existing file is opened to the beginning of both reading and writing w+ Same as w except both for reading and writing a+ Same as a except both for reading and writing Note that both the filename and mode are specified as strings. They should be enclosed in double quotation marks: Ex: FILE p1, p2; p1 = fopen ( “data”, “r”); p2= fopen ( “results”, “w”);

When the mode is writing, a file with the specified name is created if the file does not exist. The contents are deleted, if the file already exists.

When the purpose is “appending ”the file is opened with the current contents safe a file with the specified name is created if the file does not exist.

If the purpose is reading and if it exists, then the file is opened with the current contents safe otherwise an error occurs.

2.Closing a file: A file must be closed as soon as all operations on it have been completed. This ensures that all outstanding information associated with the file is flushed out from the buffers and all links to the file are broken. It also prevents any accidental misuse of the file. Syntax: fclose ( file pointer); Ex: fclose ( p1); Another instance where we have to close a file is when we went to reopen the same file in a different mode.

3.fcloseall ( ): The set of all opened files can be closed with the single function called fcloseall ( ). Syntax : fcloseall ( ); Error handling during I/O operations: It is possible that an error may occur during I/O operations on a file. The errors many include. *Trying to read beyond the end-of-file mark. *Trying to sue a file that has not been opened. *Trying to perform an operation on a file, when the file is opened for another type of operation. *Opening a file with an invalid file name. We have 2 library functions feof and ferror that can help us detect I/O errors in the files. 4. feof ( ): The feof function Can be sued to test for an end of file condition. It takes a FILE pointer as its only argument and returns a non zero integer value if all of the data from the specified file has been read, and returns zero otherwise. Ex: if ( feof ( fp)) printf ( “end of file”); 5. ferror ( ): The ferror function Reports the status of the file indicated. It also takes a FILE pointer as its argument And returns a nonzero integer if an error has been detected up to that point, during processing. It returns zero otherwise. Ex: if ( ferror ( fp) ! = 0) printf ( “An error has occurred”); * The corresponding modes of binary files are rb, wb, ab, rb+, wb+, ab+. Whenever a file is opened using open fn: a file pointer is returned. If the file cannot be opened for some reason, then the function returns a NULL pointer. Ex: if ( fp == NULL) printf ( “file could not be opened”);