Files Operations

Introduction Almost all of the program developed before this is interactive In interactive environment, input is via keyboard and output is via screen/monitor This type of processing is not suitable if it involves huge amount of input or output to be entered or be displayed on the screen at one time Therefore, file processing can solve the problem mentioned

File Declaration To implement file processing in C program, need to #include <stdio.h> FILE *in_file; FILE *out_file; in_file and out_file are known as internal file name

Opening File and fopen function Each file must be opened before it is processed While opening the file, external file name need to be related to the internal file name using fopen function. Format: internal_filename =fopen(external_filename, mode); Internal file name is the name that the C system uses to identify a file among others that a program might process External file name is the name given at “save file as” outside the program e.g. “student.dat”, “student.out” etc Mode is used to open file

File Mode Basics mode are: “r” : open file to read “w” : open file to write “a” : append data to the end of an already existing file “r+” : open and create file to update, i.e. read and write; did not overwrite previous output “w+” :open and create file for update; overwrite “a+” : append; open or create file for update

Opening File and fopen function-example FILE *in_file; FILE *out_file; in_file = fopen(“student.dat”, “r”); out_file = fopen(“student.out”, “w”);

File Open Verification There is a possibility opening file fails. Maybe the particular file does not exist Therefore need to check or verify whether the file is successfully opened If file fails to open, need to stop the program, use exit(-1); if (in_file == NULL) { printf(“File fails to open\n”); exit(-1); }

File Open Verification-cont You can also combine open file and file verification if ((in_file = fopen(“student.dat”, “r”)) == NULL) { printf(“File fails to open\n”); exit(-1); }

Closing File and fclose function Each opened file need to be closed Format: fclose(internal_filename); e.g fclose(in_file); fclose(out_file);

Check for End-of-File and the feof function Usually you don’t know how many data you want to read from file Therefore, need to check whether you have reach end of file Format: feof(internal_filename)

Check for End-of-File and the feof function-example FILE *in_file; in_file = fopen(“student.dat”, “r”); if(in_file == NULL) { printf(“Error opening file\n”); exit(-1); } while(! feof(in_file)) { //stmt to process data } fclose(in_file);

Reading Data from Text Files Format fscanf(internal file name, format control string, input list); fscanf(in_file, “%d”, &marks); fgetc(internal file name); ch = fgetc(in_file); fgets(string variable, size, internal file name); fgets(name, 10, in_file);

Writing Data to Text File Format fprintf(internal file name, format control string, output list); fprintf(out_file, “%d”, marks); fputc(character expression,internal file name); fputc(ch, out_file); fputc(“4”, out_file); fputs(string expression, internal file name); fputs(name, out_file); fputs(“makan”, out_file);

Sample Program while(!feof(in_file)) { fscanf(in_file,"%d",&marks); ++count; total = total + marks; fprintf(out_file, " %d ",marks); } avg = total /count; fprintf(out_file, "\n%.2f\n", avg); fclose(in_file); fclose(out_file); return 0; }//main #include <stdio.h> #include <stdlib.h> int main(void) { FILE *in_file; FILE *out_file; int marks, total=0, count = 0; float avg; in_file = fopen("student.dat", "r"); out_file= fopen("student.out", "w"); if(in_file == NULL) printf("Error opening file\n"); exit(-1); }

End Files Operation Q & A!