How to delete '#' symbols from a given file C - c

Question

file1
:once:echo Hello # this is a comment
:once:echo 1
:once:echo 2
:once:echo 3
:once:echo 4
Consider the file above, If I wanted to print out each line one by one how would I remove the "# this is a comment" and ':once:'
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char **argv) {
FILE *file = fopen(argv[1], "r");
char buf[100];
char p;
while (fgets(buf, sizeof(buf), file)) {
if ((p = strchr(buf, '#')))
*p = '\0';
printf("%s\n", buf);
}
fclose(file);
}
I think I can use strchr to remove the comments but unsure how to go about this.
I want the output to be this
$ gcc -Wall a.c
$ ./a.out file1
echo Hello
echo 1
echo 2
echo 3
echo 4
Current output:
:once:echo Hello # This is a comment
:once:echo 1
:once:echo 2
:once:echo 3
:once:echo 4
Unsure why the extra space is there. I think I have the right approach with the strchr just unsure how to use.

Answer 1

You should change char p; to char *p;, otherwise this is not going to work at all. If you're looking for :once: only at the start of a line, you can use strncmp() to check the first six characters, and offset the start of the string if necessary.
Also, since fgets() retains line break characters, you may as well add \n and \0 when you encounter a # symbol, and then leave out the \n when printing each line. That way your output won't be filled with double line breaks.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char **argv) {
FILE *file = fopen(argv[1], "r");
char buf[100];
char *p;
while (fgets(buf, sizeof(buf), file)) {
if ((p = strchr(buf, '#'))) {
*(p++) = '\n';
*p = '\0';
}
printf("%s", buf + (strncmp(buf, ":once:", 6) == 0 ? 6 : 0));
}
fclose(file);
}

Answer 2

This should work for you. I added a nested for inside of the while, to loop through buf and check for the '#' hash character. You should always be sure to check if the necessary file exists or not, instead of assuming that it does.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char **argv) {
FILE *file;
if (!(file = fopen(argv[1], "r"))) {
fprintf(stderr, "The specified file does not exist\n");
return 1;
}
char buf[100];
int x;
while (fgets(buf, sizeof(buf), file)) {
for (x = 0; x < sizeof(buf); x++) {
if (buf[x] == '#')
buf[x] = '\0';
}
if (strncmp(buf, ":once:", 6) == 0)
printf("%s\n", buf + 6);
else
printf("%s\n", buf);
}
fclose(file);
return 0;
}