Checking format and characters in file from stdin in C? - c

Question

I currently have a program where I read in a .txt file like so: ./myprogram < input.txt and put each character in my array. This code looks something like this:
char myArray[SIZE_ROW][SIZE_COL];
for (int i = 0; i < SIZE_ROW; i++) {
for (int j = 0; j < SIZE_COL; j++) {
fscanf(stdin, "%c ", &myArray[i][j]);
}
}
Before I fill myArray I would like to make sure that input.txt has the format of SIZE_ROW characters by SIZE_COL characters, for for example if SIZE_ROW and SIZE_COL were both equal to 4, so a valid input.txt could look something like this:
.p..
k...
..q.
.P..
while an invalid input.txt could look like this:
.....q.
..k..p
p..
While I'm checking the format, I would also like to make sure that input.txt only contains the characters q, k and p for example.
I have tried using fgets() to read in the file line by line, but when I do this, using scanf afterwards to fill myArray seems to not work. I also do not know the name of the file beforehand, so the only way I can open it is as shown above: ./myprogram < input.txt.

Answer 1

Some pseudo code to get you started.
int Read_EsoFile(char myArray[RSIZE][CSIZE], FILE *istream) {
for each row (0 to RSIZE -1)
char buf[CSIZE+3];
read line using fgets and detect EOF
truncate potential trailing \n
test if valid
length == CSIZE?
elmenet only `q k p`?
save in myArray[i]
return success status
}
// example usage
char myArray[RSIZE][CSIZE];
int result = Read_EsoFile(myArray, stdin);

Answer 2

I also do not know the name of the file beforehand, so the only way I can open it is as shown above: ./myprogram < input.txt.
If you do not know the name of the file beforehand, the only way to open it is not: ./myprogram < input.txt. You can use command line arguments to open the file using its name which is passed as a command line argument at runtime, like: ./myprogram input.txt.
Here is the code to do that, plus I have also applied all the checks that you asked for and then applied your code to get the data into the array and printed the array in the end to verify the contents:
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define SIZE_ROW 4
#define SIZE_COL 4
int main(int argc, char* argv[])
{
if(argc == 2)
{
FILE *f = fopen(argv[1], "r");
char* buffer = NULL;
size_t n = SIZE_COL;
int rows = 0, cols;
int flag = 1;
int i, j;
while(!feof(f))
{
getline(&buffer, &n, f);
if(strlen(buffer) > 1) // to skip blank lines
{
cols = strlen(buffer)-1;
if(cols != SIZE_COL)
{
break;
}
for(i=0; i<cols; i++)
{
if(!(buffer[i] == '.' || buffer[i] == 'q' || buffer[i] == 'Q' || buffer[i] == 'k' || buffer[i] == 'K' || buffer[i] == 'p' || buffer[i] == 'P'))
{
break;
}
}
if(i<cols)
{
flag = 0;
break;
}
rows++;
free(buffer);
buffer = NULL;
}
}
if(flag)
{
if(cols == SIZE_COL)
{
if(rows == SIZE_ROW)
{
rewind(f);
char myArray[SIZE_ROW][SIZE_COL];
for (i = 0; i < SIZE_ROW; i++)
{
for (j = 0; j < SIZE_COL; j++)
{
fscanf(f, "%c ", &myArray[i][j]);
}
}
for (i = 0; i < SIZE_ROW; i++)
{
for (j = 0; j < SIZE_COL; j++)
{
printf("%c ", myArray[i][j]);
}
printf("\n");
}
}
else
{
printf("Row size is not %d.\n", SIZE_ROW);
}
}
else
{
printf("Column size is %d not %d.\n", cols, SIZE_COL);
}
}
else
{
printf("Invalid characters in file.\n");
}
fclose(f);
}
else
{
printf("Invalid Arguments! Please give file name as argument from command line.\n");
}
return 0;
}
Ask me, if you do not understand anything in the code. You should call it like:
./myprogram input.txt