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Data Files

Data Files. Allow us to store information permanently, and access and alter information whenever necessary Types of data files Stream-oriented (Standard) data files: Easier to work with Text file: consisting of consecutive characters

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Data Files

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  1. Data Files • Allow us to store information permanently, and access and alter information whenever necessary • Types of data files • Stream-oriented (Standard) data files: Easier to work with • Text file: consisting of consecutive characters • Binary file (unformatted data files): organizes data into blocks. These blocks represent more complex data structure, such as arrays and structures • System-oriented data files: closely related to the computer’s operating system

  2. Opening and closing a data file • First establish a buffer area, where information is temporarily stored while being transferred between the computer’s memory and the data file FILE *ptvar; • FILE is a special structure type that establishes the buffer area, ptvar is pointer (stream pointer or stream) that indicates the beginning of the buffer area.

  3. Opening and closing a data file • Data files must be opened before it is created or processed. This associates the file name with buffer area (i.e. with the stream) • It also specifies how the data file will be utilized, as • Read-only file • Write-only file • Read/write file Ptvar=fopen(file-name, file-type);

  4. Opening and closing a data file • File name is a string, that specifies the name (also location) of the file • File-type must be one of the following string: • “r” =read only file • “w”=write only file. Destroy existing same name file • “a”=file for appending. New file created (if no file) • “r+”=both read and write file • “w+”=both read and write file. Destroy existing file. • “a+”=file for reading and appending. New file create

  5. Opening and closing a data file • fopen function returns a pointer to the beginning of the buffer area associated with file. (returns NULL is file does not exist) • Data files must be closed at the end of the of the program fclose(ptvar)

  6. Reading and writing a data file • putc(“a”, fpt): put a character into a data file • c=getc(fpt):read a character from a data file • fprintf(fpt,”%s”,custome.name): write the value of a variable into a file • fscanf(fpt,”%s”, customer.name): read a value from a file and store in a variable • feof(fpt):check whether end-of-file has been reached or not

  7. Reading and writing unformatted data file • fwrite(&customer, sizeof(record),1,fpt): write a block of data stored in the variable customer, whose data type is record, in the file fpt 1 time • fread(&customer, sizeof(record),1,fpt): read a block of data stored in the variable customer, whose data type is record, from the file fpt 1 time

  8. Problems • Take input from keyboard and store in a file • Read from a file and display in the monitor • Copy a file • Encoding and decoding a file • Create a file containing customer record • Creating an unformatted data file containing customer record

  9. Some more functions related to file • fseek: seek a position and reposition the file pointer of a strean • remove: delete a file • ftell: return the current file pointer.Used to find the size of a file

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