File handling C program
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The document outlines file handling in C, explaining that a file is a location on disk for storing related data and describing basic file operations such as opening, reading, writing, and closing files. It differentiates between low-level and high-level I/O operations and specifies functions like fopen, fclose, getc, and fprintf for file manipulation. Additionally, it covers file modes for reading, writing, and appending, and emphasizes the importance of closing files to prevent data loss and resource limitations.
File handling C program
- 1. For more Https://www.ThesisScientist.com Unit 10 File Handling What is a File? Wherever there is a need to handle large volumes of data, it is advantageous to store data on the disks and read whenever necessary. This method employs the concept of files to store data. A file is a place on disk where a group of related data is stored. C supports a number of functions that have the ability to perform basic file operations, which include: naming a file opening a file reading data from a file writing data to a file closing a file There are two distinct ways to perform file operations in C. 1. Low level I/O Operation (It uses operating system calls) 2. High level I/O Operation (It uses functions in C's Standard I/O library) Table 10.1: List of High Level I/O Functions Function Name Operation fopen() Creates a new file for use or opens an existing file for use. fclose() Closes a file which has been opened for use. getc() Reads a character from a file. putc() Writes a character to a file. fprintf() Writes a set of data values to a file. fscanf() Reads a set of data values from a file. getw() Reads an integer from a file. putw() Writes an integer to a file. Defining and Opening a File Following is the general format for declaring and opening a file: File *fp; fp = fopen ( "filename", "mode"); The first statement declares the variable fp as a "pointer to the data type FILE".
- 2. The second statement opens the file named filename and assigns an identifier to the FILE type pointer fp. This pointer which contains all the information about the file is subsequently used as a communication link between the system and the program. The second statement also specifies the purpose of opening this file. The mode does this job. Mode can be one of the following: r Opens the file for reading only. w Opens the file for writing only. a Opens the file for appending (or adding) data to it. Both the filename and mode are specified as string. They should be enclosed in double quotation marks. Depending on the mode specified, one of the following actions may be performed: 1. 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. 2. 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. 3. If the purpose is 'reading', and if it exists, then the file is opened with the current contents safe, otherwise an error occurs. Closing a File Once all the operations on a file have been completed, the file is closed. This is done to clear the buffers and flush all the information associated with the file. It also prevents any accidental misuse of the file. In case there is a limit to the number of files that can be kept open simultaneously, closing of unwanted files might help open the required files. When there is a need to use a file in a different mode, the file has to be first closed and then reopened in a different mode. The I/O library supports a function for this of the following form: fclose (file_pointer); This would close the file associated with the file pointer file_pointer. e.g.: ......... FILE *p1, *p2; p1 = fopen ("INPUT", "w"); p2 = fopen ("OUTPUT", "r"); ......... fclose(p1); fclose(p2);
- 3. This program opens two files and closes them after all operations on them are completed. Input/Output Operations on Files getc & putc Functions These are analogous to getchar and putchar functions and can handle only one character at a time. putc can be used to write a character in a file opened in write mode. A statement like putc (ch, fp1); writes the character contained in the character variable ch to the file associated with file pointer fp1. Similarly, getc is used to read a character from a file that has been opened in read mode. The statement c = getc(fp2); would read a character from the file whose file pointer is fp2. The file pointer moves by one character position for every operation of getc or putc. The getc will return an end-of-file marker EOF, when end of the file has been reached. The reading should be terminated when EOF is encountered. Testing for the end-of-file condition is important. Any attempt to read past the end of file might either cause the program to terminate with an error or result in an infinite loop situation. getw & putw Functions The getw and putw are integer-oriented functions. They are similar to the getc and putc functions and are used to read and write integer values on UNIX systems. The general forms of getw and putw are: putw (integer, fp); & getw (fp); fprintf & fscanf Functions The functions fprintf and fscanf perform I/O operations that are identical to the familiar printf and scanf functions. The general syntax of fprintf is fprintf (fp, "control string", list); where fp is a file pointer associated with a file that has been opened for writing. The control string contains output specifications for items in the list. The list may include variables, constants and strings. e.g.: fprintf (f1,"%s %d %f", name, age, 7.5); here name is an array variable of type char and age in an int variable. The general syntax of fscanf is fscanf (fp, "control string", list); This statement would cause the reading of the items in the list from the file specified by fp, according to the specifications contained in the control string. e.g.: fscanf (f2, "%s %d", item, &quantity);