CSPP 50101 - Lab 6

This lab contains a simple module of some file processing functions. The code for these function is organized into two different files:

• myfileio.h: A header file that contains function declarations of four functions: show_file(), count_lines(), get_values(), and write_columns()
• myfileio.c: A source file that contains an implementation of show_file(). (You will implement the other three functions in this lab).

  int show_file(char * filename);

The file demo.c has a function main() that calls and tests show_file():

int main(int argc, char ** argv)
{
  if (argc != 2)
  {
    printf("Usage: %s filename\n", argv[0]);
    exit(1);
  }

  show_file(argv[1]);

  return 0;
}

  #include "myfileio.h"

Next, to compile code in myfileio.c and demo.c into a single executable, we include both files as input to gcc. (You do not need to include .h header files as input to gcc.)

$ gcc -Wall -std=c99 myfileio.c demo.c -o demo

$ ./demo in1.txt
Calling show_file() ...
100
110
120
125
130

Preventing multiple inclusions of a header file

 
   #ifndef MYFILEIO_H 
   #define MYFILEIO_H

   /* Print contents of file to stdout. 
    * Returns -1 if error occurs, 0 otherwise */
   int show_file(char * filename);
 
   ...
 
   #endif

File I/O

int show_file(char * filename)
{
  FILE * fp;
  char ch;

  if( (fp=fopen(filename,"r")) == NULL)
    return -1;

  while ((ch=getc(fp)) != EOF)
    putchar(ch);

  fclose(fp);

  return 0;
}

  if( (fp=fopen(argv[1],"r")) == NULL)
    return -1;

  while ((ch=getc(fp)) != EOF)
    putchar(ch);  

Exercise 1

You are already provided with this function prototype in myfileio.h:

  /* Returns count of lines in file, or -1 if error occurs */
  int count_lines(char * filename);

You can use file test_ex1.c to test your implementation of count_lines(). This program reads the name of an input file from the command line and passes this as an argument to count_lines(). Then the return value of count_lines() is displayed. You can use files in1.txt and in2.txt as sample input files.

You do not need to make any changes to test_ex1.c; it should work as-is with your version of count_lines().

Remember to compile both test_ex1.c and myfileio.c into a single executable:

$ gcc -Wall -std=c99 myfileio.c test_ex1.c -o test_ex1

$ ./test_ex1 in1.txt
Number of lines in in1.txt: 5
$ wc -l in1.txt
       5 in1.txt

Reading from a file with fprintf()

The file fscanfdemo.c shows an example of a call to fscanf(). Here an integer is read from an open file:

  int val;
  fscanf(fp,"%d",&val);

get_values() should not call free(); you can assume that the calling function will do then when it not longer needs the array that is returned.

get_values() should return NULL if a malloc() error occurs. If a scanf() error occurs, the function should return NULL and free any memory that it has already allocated with malloc (otherwise you may have a memory leak).

You are given this function prototype in myfileio.h:

/* Reads n integer values from filename, returns result in dynamically 
 * allocated array, or returns NULL if error occurs */
int * get_values(char * filename, unsigned int n);

Use the file test_ex2.c to test your implementation of get_values(). In this program, the function main() uses count_lines() from Exercise 1 to compute n, the number of lines in the input file. Then, get_values() is called to read n integers from the input file.

You can use input files in1.txt to test your program:

$ ./test_ex2 in1.txt
Number of lines in in1.txt: 5
Printing values in in1.txt ...
100
110
120
125
130

Writing output to a file

gcc -Wall -std=c99 writedemo.c -o writedemo
$ ./write
Writing to file write.txt ...
$ cat write.txt
Hello cspp50101!

int main(int argc, char ** argv)
{
  FILE * fp;

  if( (fp=fopen("write.txt","w")) == NULL)
  {
    printf("Can't open file write.txt for writing.\n");
    exit(1);
  }

  printf("Writing to file write.txt ...\n");

  fprintf(fp,"Hello cspp50101!\n");

  fclose(fp);

  return 0;
}

Exercise 3

As with the previous exercises, you are given this function prototype in myfileio.h, and you only need to update myfileio.c with your implementation of this function:

/* Writes n values in arr to new file in 2 columns.
 * Returns -1 if error occurs, 0 otherwise */
int write_columns(int * arr, unsigned int n, char * filename);

You are given the file test_ex3.c to test your implementation of write_columns(). This program takes the name of the input and output files as command line arguments:

$ gcc -Wall -std=c99 myfileio.c test_ex3.c -o test_ex3
$ ./test_ex3 in1.txt out1.txt 
Number of lines in in1.txt: 5
Displaying output file out1.txt...
100	125
110	130
120

Submitting your assignment

For this lab you only need to submit file myfileio.c, which should have implementations of these functions:

• Exercise 1: count_lines()
• Exercise 2: get_values()
• Exercise 3: write_columns()

Be sure that every source file you submit includes this information in comments at the top of the file:

• Your first and last name
• Your username
• Any other comments you want to add about your program (optional)

Also include a simple README file in your lab6 directory. This file should include your first and last name, your username, the list of files that you are submitting, and any other comments or questions for the Lab TA.

Do not submit any compiled binary files

You will submit this lab with the hwsubmit program.

$ hwsubmit cspp50101lab <path to your lab6 directory>

prepared by Sonjia Waxmonsky