How to get input from bash terminal into my program - c

Question

One of my assignments has the following question:
One function (function #2) of your program is to read in the content of an instance file. To read in
the file "
instance10
001.txt
" you will execute the command:
NameOfProgram -i instance10
001.txt
Here "
-i " is the command-line option that indicates the succeeding argument is the
input filename.
This is what I have done so far, mostly a skeleton:
/* Assignment 1 */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
int main(int argc, char *argv[])
{
FILE *fp;
int max_x, max_y, num_pt, rand_inst;
int *x_coordinate, *y_coordinate;
int inputfile = 0, outputfile = 0;
int i;
if (argc == 1)
{
/* to generate random instances, accepting parameters from stdin */
printf("Generating random instances...");
printf("Enter the circuit board size MAX_X MAX_Y: ");
scanf("%d %d", &max_x, &max_y);
printf("Enter the number of points NUM_PT: ");
scanf("%d", &num_pt);
printf("Enter the number of random instances to be generated: ");
scanf("%d", &rand_inst);
return 1;
}
for (i = 1; i < argc; i++)
{
if (strcmp (argv[i], "-i") == 0)
inputfile = i+1;
else if (strcmp (argv[i], "-o") == 0)
outputfile = i+1;
}
if (inputfile == 0)
{
/* invalid comman line options */
printf("\nIncorrect command-line\n");
printf("myprogram [-i inputfile [-o outputfile]]");
return -1;
}
**/* THIS IS WHERE I NEED HELP */**
if (inputfile == 1)
{
fp = fopen(/*Name of the input file (instance10_001.txt) */, "r")
}
if ((fp = fopen(argv[inputfile], "r")) == NULL)
{
/* open file error */
return -2;
}
while (fscanf(fp, "%d", &max_x) != 1)
{
if (ferror(fp))
{
/* read error */
fclose(fp);
return -3;
}
if (feof(fp))
{
/* no integer to read */
fclose(fp);
return -4;
}
fscanf(, "%*[^\n]"); /*skip the rest of line */
}
if (fscanf(fp, "%d", &max_y) != 1)
{
/* max_y not following max_x */
fclose(fp);
return -5;
}
while (fscanf(fp, "%d", &num_pt) != 1)
{
if(ferror(fp))
{
/* read error */
fclose(fp);
return -6;
}
if (feof(fp))
{
/* no integer to read */
fclose(fp);
return -7;
}
fscanf(fp, "%*[^\n]"); /* skip the rest of line */
}
x_coordinate = (int *)malloc(num_pt * sizeof(int));
y_coordinate = (int *)malloc(num_pt * sizeof(int));
for (i = 0; i < num_pt; i++)
{
while (fscanf(fp, "%d", &x_coordinate[i]) != 1)
{
if (ferror(fp))
{
/* read error */
fclose(fp);
return -8;
}
if (feof(fp))
{
/* no integer to read */
fclose(fp);
return -9;
}
fscanf(fp, "%*[^\n]"); /* skip the rest of line */
}
if (fscanf(fp, "%d", &y_coordinate[i]) != 1)
{
/* y_coordinate not following x_coordinate */
fclose(fp);
return -10;
}
}
fclose(fp);
if (outputfile > 0)
{
if ((fp = fopen(argv[outputfile], "w")) == NULL)
{
/* open file error */
return -2;
}
fprintf(fp, "##################################################\n");
fprintf(fp, "#%s\n", argv[inputfile]);
fprintf(fp, "#area [0, MAX_X] x [0, MAX_Y]\n");
fprintf(fp, "%d\t%d\n", max_x, max_y);
fprintf(fp, "#number of points NUM_PT\n");
fprintf(fp, "%d\n", num_pt);
fprintf(fp, "#coordinates\n");
for (i = 0; i < num_pt; i++)
{
fprintf(fp, "%d\t%d\n", x_coordinate[i], y_coordinate[i]);
}
fprintf(fp, "#end of instance\n");
fclose(fp);
}
else
{
printf("##################################################\n");
printf("#%s\n", argv[inputfile]);
printf("#area [0, MAX_X] x [0, MAX_Y]\n");
printf("%d\t%d\n", max_x, max_y);
printf("#number of points NUM_PT\n");
printf("%d\n", num_pt);
printf("#coordinates\n");
for (i = 0; i < num_pt; i++)
{
printf("%d\t%d\n", x_coordinate[i], y_coordinate[i]);
}
printf("#end of instance\n");
}
free(x_coordinate);
free(y_coordinate);
return 0;
}
I am wondering how I can read the name of the input file from bash terminal. Should I use scanf?
how do I get what the user has inputted as the input file? Like for example if the user is running my program from bash with ./myprogram -i instance10_001.txt, how can I open the inputted file in my program?
PS I am using my Ubuntu terminal to access my lab computer via ssh.
Language: c99 ; Compiler: gcc

Answer 1

This looks like a simple error in your if statment. You're saying if, and only if, inputfile is 1 (which means -o must have been argv[0]) it will open inputfile.
if (inputfile == 0)
{
/* invalid command line options */
printf("\nIncorrect command-line\n");
printf("myprogram [-i inputfile [-o outputfile]]");
return -1;
}
else /* if inputfile is not equal to 0, then this will execute. */
{
fp = fopen(argv[inputfile], "r");
}
Also, there's another problem here, in which you assign fp to a function and then reopen the file already opened in fp:
/* removed fp = fopen (a function) */
if (fp == NULL) /* You already opened the file; no need to open again until fclose */
{
/* open file error */
return -2;
}
Also, in this block of code:
while (fscanf(fp, "%d", &x_coordinate[i]) != 1)
{
if (ferror(fp))
{
/* read error */
fclose(fp);
return -8;
}
if (feof(fp))
{
/* no integer to read */
fclose(fp);
return -9;
}
fscanf(fp, "%*[^\n]"); /* skip the rest of line */
}
Fscanf returns the number of arguments successfully filled, which in this case, will always be 1.
Note that similar problems may be present in the remainder of the code.