Reading a line and removing Spaces from matrix in a file - c

Question

OK so I manage to write to the file char by char but it writes twice the numbers and it it still write it with spaces. Any advice and solution?
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <unistd.h>
#include <ctype.h>
#include <fcntl.h>
extern int errno;
#define MAX_LEN 18
int main(int argc, char *argv[]) {
int fd[2], des, bytes, target;
char buffer[161];
int fdr, fdw; // file descriptors
char c;
fdr = open(argv[1], O_RDONLY); // open files
fdw = open("gg.txt", O_WRONLY | O_CREAT);
if (fdr < 0 || fdw < 0) {
perror("failed to open input or output files");
exit(EXIT_FAILURE);
}
while (read(fdr, &c, 1)) { // read/write a single char from/to the files
if (c != ' ' && c != EOF) {
if (write(fdw, &c, 1) != 1) {
perror("write() failed");
exit(EXIT_FAILURE);
}
} // echo char to stdout
}
close(fdr); // close the files
close(fdw);
exit(EXIT_SUCCESS);
}
EDIT SECTION
hey again,
i managed to read the file and write it to new one without spaces but i'm trying to insert the values to matrix but im getting an error trying to open the new file.
i have changed the permissions
fdw = open("gg.txt", O_RDWR | O_CREAT | O_TRUNC, 0644);
the function
void removeSpaces(int matrix[SIZE][SIZE],int fdr, int fdw) {
char c;
char matBuffer={0};
while (read(fdr, &c, 1)) // read/write a single char
{ // from/to the files
if (c != ' ') {
if (write(fdw, &c, 1) != 1) {
perror("write() failed");
exit(EXIT_FAILURE);
}
}
}
int i;
int j;
int k=0;
while(read(fdw, &matBuffer, 1))
{
for(i=0;i<SIZE;i++)
{
for(j=0;j<SIZE;j++)
{
matrix[i][j]=matBuffer-'0';
k++;
}
k=0;
}
}
}
The whole program
// C program to illustrate
// open system call
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <unistd.h>
#include <ctype.h>
#include <fcntl.h>
#define MAX_LEN 18
#define SIZE 9
void removeSpaces(int matrix[SIZE][SIZE],int fdr, int fdw) {
char c;
char matBuffer={0};
while (read(fdr, &c, 1)) // read/write a single char
{ // from/to the files
if (c != ' ') {
if (write(fdw, &c, 1) != 1) {
perror("write() failed");
exit(EXIT_FAILURE);
}
}
}
int i;
int j;
int k=0;
while(read(fdw, &matBuffer, 1))
{
for(i=0;i<SIZE;i++)
{
for(j=0;j<SIZE;j++)
{
matrix[i][j]=matBuffer-'0';
k++;
}
k=0;
}
}
}
int is_safe(int matrix[9][9],int n, int r, int c)
{
int i,j;
//checking in row
for(i=0;i<9;i++)
{
//there is a cell with same value
if(matrix[r][i] == n)
return 0;
}
//checking column
for(i=0;i<SIZE;i++)
{
//there is a cell with the value equal to i
if(matrix[i][c] == n)
return 0;
}
//checking sub matrix
int row_start = (r/3)*3;
int col_start = (c/3)*3;
for(i=row_start;i<row_start+3;i++)
{
for(j=col_start;j<col_start+3;j++)
{
if(matrix[i][j]==n)
return 0;
}
}
return 1;
}
int main(int argc, char * argv[]) {
int pipe_descs[2];
int matrix[SIZE][SIZE];
int fdr, fdw; // file descriptors
int i,j;
/* if (pipe(pipe_descs) == -1) {
fprintf(stderr, "cannot open");
exit(1);
}
pid_t status = fork();
if(status ==0 )
{
}*/
fdr = open(argv[1], O_RDONLY); // open files
fdw = open("gg.txt", O_RDWR | O_CREAT | O_TRUNC, 0644);
if (fdr < 0 || fdw < 0) { //validation for error
perror("failed to open input or output files");
exit(EXIT_FAILURE);
}
removeSpaces(matrix,fdr, fdw);
for(i=0; i<9; i++){ /* Iterate of each row */
for(j=0; j<9; j++){ /* In each row, go over each col element */
printf("%c ",matrix[i][j]); /* Print each row element */
}
printf("\n"); /* Finish a row, start a new line */
}
close(fdr); // close the files
close(fdw);
exit(EXIT_SUCCESS);
}

Answer 1

There are multiple problems in the code:
you do not test for read errors, read can return -1 for error, which would not stop the while loop.
testing c != EOF is meaningless. EOF is returned by getc() to indicate end of stream or input error, read indicates these conditions in its return value, c is always a byte value if read succeeded and returned 1.
gg.txt is not truncated by open with the given flags. Chances are you are overwriting the beginning of the file and for some reason the file is longer from previous attempts and still contains previously written data. You must also pass the mode bits for the file creation as the third argument to open. Use this:
// open the file for writing, truncate if it exists or create with
// read/write permission for user, read permission for group and others
fdw = open("gg.txt", O_WRONLY | O_CREAT | O_TRUNC, 0644);
the comment // echo char to stdout does not seem to refer to any code.
Here is a corrected version:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/types.h>
#include <unistd.h>
int main(int argc, char *argv[]) {
int fdr, fdw; // file descriptors
char c;
fdr = open(argv[1], O_RDONLY); // open files
if (fdr < 0) {
fprintf(stderr, "failed to open input file %s: %s\n", argv[1], strerror(errno));
return EXIT_FAILURE;
}
// open the output file for writing, truncate if it exists or create with
// read/write permission for user, read permission for group and others
fdw = open("gg.txt", O_WRONLY | O_CREAT | O_TRUNC, 0644);
if (fdw < 0) {
fprintf(stderr, "failed to open output file %s: %s\n", "gg.txt", strerror(errno));
return EXIT_FAILURE;
}
// read/write a single char from/to the files
while (read(fdr, &c, 1) == 1) {
if (c != ' ') {
if (write(fdw, &c, 1) != 1) {
perror("write() failed");
return EXIT_FAILURE;
}
}
}
close(fdr); // close the files
close(fdw);
return EXIT_SUCCESS;
}