11Input/Output and Files2Introduction• Data files– When you use a file to store data for use by a program, that file usually consists of text (alphanumeric data) and is therefore called a text file.– Can be created, updated, and processed by C programs – Are used for permanent storage of large amounts of data• Storage of data in variables and arrays is only temporary3Files and Streams• C views each file as a sequence of bytes– File ends with the end-of-file marker• Stream created when a file is opened– Provide communication channel between files and programs– Opening a file returns a pointer to a FILEstructure• Example file pointers:• stdin - standard input (keyboard)• stdout - standard output (screen)• stderr - standard error (screen)4Files and Streams• Read/Write functions in standard library– fgetc• Reads one character from a file• Takes a FILE pointer as an argument• fgetc( stdin ) equivalent to getchar()– fputc• Writes one character to a file• Takes a FILE pointer and a character to write as an argument• fputc( 'a', stdout ) equivalent to putchar('a' )– fscanf / fprintf• File processing equivalents of scanf and printf25Creating a Sequential File• Creating a File– FILE *myPtr;• Creates a FILE pointer called myPtr– myPtr = fopen("myFile.dat", openmode);• Function fopen returns a FILE pointer to the file specified• Takes two arguments – file to open and file open mode• If open fails, NULL returned– fprintf• Used to print to a file• It is like printf, except first argument is a FILE pointer (pointer to the file you want to print in)6Creating a Sequential File• Typical file open modes:Mode Description r Open a file for reading. w Create a file for writing. If the file already exists, discard the current contents. a Append; open or create a file for writing at end of file. 7Creating a Sequential File– feof( FILE pointer )• Returns true if end-of-file indicator (no more data to process) is set for the specified file– fclose( FILE pointer )• Closes specified file• Performed automatically when program ends• Good practice to close files explicitly• Details– Programs may process no files, one file, or many files– Each file must have a unique name and should have its own pointer81 /* 2 Create a sequential file */3 #include <stdio.h>45 int main()6 { 7 int account;8 char name[ 30 ];9 double balance;10 FILE *cfPtr; /* cfPtr = clients.dat file pointer */1112 if ( ( cfPtr = fopen( "clients.dat", "w" ) ) == NULL )13 printf( "File could not be opened\n" );14 else { 15 printf( "Enter the account, name, and balance.\n" );16 printf( "Enter EOF to end input.\n" );17 printf( "? " );18 scanf( "%d%s%lf", &account, name, &balance );1920 while ( !feof( stdin ) ) { 21 fprintf( cfPtr, "%d %s %.2f\n", 22 account, name, balance );23 printf( "? " );24 scanf( "%d%s%lf", &account, name, &balance );25 }2627 fclose( cfPtr );28 }2930 return 0;31}39Program OutputEnter the account, name, and balance.Enter EOF to end input.? 100 Jones 24.98? 200 Doe 345.67? 300 White 0.00? 400 Stone -42.16? 500 Rich 224.62?10Reading Data from a File• Reading a sequential access file– Create a FILE pointer, link it to the file to readmyPtr = fopen( "myFile.dat", "r" );– Use fscanf to read from the file• Like scanf, except first argument is a FILEpointerfscanf( myPtr, "%d%s%f", &myInt, &myString, &myFloat );– Data read from beginning to end1112 /* Reading and printing a sequential file */3 #include <stdio.h>45 int main()6 { 7 int account;8 char name[ 30 ];9 double balance;10 FILE *cfPtr; /* cfPtr = clients.dat file pointer */1112 if ( ( cfPtr = fopen( "clients.dat", "r" ) ) == NULL )13 printf( "File could not be opened\n" );14 else { 15 printf( "%-10s%-13s%s\n", "Account", "Name", "Balance" );16 fscanf( cfPtr, "%d%s%lf", &account, name, &balance );1718 while ( !feof( cfPtr ) ) { 19 printf( "%-10d%-13s%7.2f\n", account, name, balance );20 fscanf( cfPtr, "%d%s%lf", &account, name, &balance );21 }2223 fclose( cfPtr );24 }2526 return 0;27 }Account Name Balance100 Jones 24.98200 Doe 345.67300 White 0.00400 Stone -42.16500 Rich 224.62 12Example: Merge two files#include <stdio .h>int main() { FILE *fileA , /* first input file */*fileB, /* second input file */*fileC; /* output file to be created */int num1, /* number to be read from first file */num2; /* number to be read from second file */int f1, f2;/* Open files for processing */fileA = fopen("class1.txt","r");fileB = fopen("class2.txt","r");fileC = fopen("class.txt","w");413/* As long as there are numbers in both files, read and compare numbersone by one. Write the smaller number to the output file and read the next number in the file from which the smaller number is read. */f1 = fscanf( fileA, "%d", &num1);f2 = fscanf( fileB, "%d", &num2);while ((f1!=EOF) && (f2!=EOF)){if (num1 < num2){fprintf( fileC,"%d\n", num1);f1 = fscanf( fileA , "%d", &num1);}else if (num2 < num1) {fprintf( fileC,"%d\n", num2);f2 = fscanf( fileB , "%d", &num2);}else { /* numbs are equal:read from both files */fprintf( fileC,"%d\n", num1);f1 = fscanf( fileA , "%d", &num1);f2 = fscanf( fileB , "%d", &num2);}}14while (f1!=EOF){/* if reached end of second file, read the remaining numbers from first file and write to output file */fprintf(fileC,"%d\n", num1);f1 = fscanf(fileA, "%d", &num1);}while (f2!=EOF){ if reached the end of first file, read the remaining numbers from second file and write to output file */fprintf(fileC,"%d\n", num2);f2 = fscanf(fileB, "%d", &num2);}/* close files */fclose(fileA);fclose(fileB);fclose(fileC);return 0;} /* end of main */15Character I/O• Suppose you want to store a set of quotations from Shakespeare in a file named hamlet.txt.To be, or not to be: that is the question. Whether ‘tis nobler in the mind to suffer The slings and arrows of outrageous fortune,Or to take arms against a sea of troubles,And by opposing end them?16Text Files• You might think of the file hamlet.txtas consisting of five lines. Internally however, text files are represented as a sequence of characters including the ‘\n’.517/* This program copies one file to another using character I/O */#include <stdio.h>void CopyFile(FILE *infile, FILE *outfile);FILE *OpenUserFile(char *prompt, char *mode);int main(){FILE *infile, *outfile;printf("This program copies one file to another.\n");infile =