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File Input/Output

File Input/Output. File information. Name z:Visual Studio 2005Projects fileio fileio myinput.txt \file-svr-1classECE-160pviallmyoutput.txt Read/Write Type (binary or ASCII text) Access (security; single/multiple user) Position in file

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File Input/Output

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  1. File Input/Output

  2. File information • Name z:\Visual Studio 2005\Projects\fileio\fileio\myinput.txt\\file-svr-1\class\ECE-160\pviall\myoutput.txt • Read/Write • Type (binary or ASCII text) • Access (security; single/multiple user) • Position in file • All above info is stored in a FILE type variable, pointed to by a file handle

  3. File i/o function calls fopen(filename, file_access) • filename: is name of file • file_access is: “r+t” for reading text file“w+t” for writing text file many other options available • returns:file_handle, that is the address of FILE (a FILE *) on successNULL (zero) on failure

  4. File i/o function calls fclose(file_handle) • Closes a file • This is recommended for input files (to free up system resources) • This is required for output files (as often times the O/S does not write the last bit of a file out to the disk until the file is closed

  5. File i/o function calls fprintf(file_handle, format_specifier, 0 or more variables) • file_handle: is address returned by openf() • format_specifier: same as for printf() • 0 or more variables: same as printf()

  6. Sample program • Read three integer values from the file myinput.txt • Determine sum and average • Write the original three values as well as the sum and average to the file myoutput.txt

  7. The program (part 1) #define _CRT_SECURE_NO_DEPRECATE #include <stdio.h> #include <stdlib.h> void main() { FILE *infile; FILE *outfile; intx,y,z,sum; float avg; // Open input file, exit if error infile=fopen("myinput.txt","r+t"); if (infile==NULL) { printf("Error opening myinput.txt\n"); exit(0); } // Generally file opens are done as below if ((outfile=fopen("myoutput.txt","w+t"))==NULL) { printf("Error opening myoutput.txt\n"); exit(0); }

  8. The program (part 2) // read the three values // its a good idea to account for \n's in the file fscanf(infile,"%d\n",&x); fscanf(infile,"%d\n",&y); fscanf(infile,"%d\n",&z); // sum and avg sum = x+y+z; avg = (float)sum/3.0; // print out values fprintf(outfile,"Values: %d, %d, %d\n",x,y,z); fprintf(outfile,"Sum: %d\n",sum); fprintf(outfile,"Avg: %7.2f\n",avg); // close the files fclose(infile); fclose(outfile); }

  9. Adding a text file to the project (way 1) Use a text editor (notepad, wordpad, etc) to create a text file. Save the file in the proper directory. If your project is named fileio, the proper directory and filename would be: Z:\Visual Studio 2005\Projects\fileio\fileio\myinput.txt

  10. Adding a text file to the project (way 2) • Project • Add new item • Utility • Text file • Enter file name This creates another tab where you may input your myinput.txt file

  11. Viewing your myoutput.txt file (way 2) • Project • Add existing item • Change file type to all files • Click myoutput.txt – this will cause myoutput.txt to appear in the file list on the left • Enter file name This creates another tab where you may input your myinput.txt file

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