C Programming Language

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How to print each line from a string (reddthat.com)

submitted 1 week ago by dr_robotBones@reddthat.com to c/c_lang@programming.dev

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I'm trying to make some sort of simple console text editor program to get better with C. I'm having trouble with what I thought would be a somewhat simple task:

How do I get each line from my char* buffer, which contains all of my text, so I can output each line, including empty lines, with the correct line number in front of it.

I tried several different ways already, but none have stuck. I tried strtok(), which is what is currently pushed to my repo, and it ignores whitespace. I tried strchr() but did not have the slightest idea how that function worked and got an infinite loop. I tried doing my own function to create an array of lines but that lead to a segmentation fault which was not fixed by mallocing the array. I am at a loss here, I'm not sure what I can do.

Here is the repo: https://codeberg.org/Mister_Bones/txt-ed

Here is the offending code:

// Print contents of file
int print_file(char* buffer) {
	// Print a new line
	printf("\n");

	// Print each line with line number
	// Set first line
	int line_num = 1;

	// Get individual line from buffer
	char* line = strtok(buffer, "\n");

	// Loop through and print lines
	// TODO: Don't ignore whitespace
	while (line != NULL) {
		printf("%4d\t%s\n", line_num, line);
		line = strtok(NULL, "\n");
		line_num++;
	}

	return 0;
}

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[–] oantby@lemmy.today 2 points 1 week ago* (last edited 1 week ago) (1 children)

the strtok issue is, per the man page, that strtok returns only “non empty” tokens with your given delimiters.

Given only one delimiter, the strchr approach is likely what I'd use. understanding strchr (and the similar strstr) is a pretty useful thing to have anyway, so it’s a good time to learn it. strchr makes no modifications and isn’t aiming to make tokens for you. It is looking for the first instance of a given byte in a C string and, provided it found it, returning you a pointer to that byte. as such, if it returns you something other than NULL, you’ve got a pointer to a byte. assuming you’re fine with the function modifying the buffer, you can convert that byte to a nul byte (\0), then print buffer, then a new line. You then advance your buffer pointer to the byte past the now-nul byte. Continue until strchr returns NULL, which is your last line - assuming the buffer is nul-terminated

Edit: example, now that I've got a real keyboard:

void strchr_loop(char *buf) {
    char* p;
    while ((p = strchr(buf, '\n')) != NULL) {
        *p = '\0';
        printf("Line = %s\n", buf);
        buf = p + 1;
    }
    printf("Last line = %s\n", buf);
}

[–] dr_robotBones@reddthat.com 1 points 1 week ago

I see , thank you for the example, I think I've come up with a way I can use strchr for my purposes.

Also, I've heard of there being man pages for C library functions before, is there a way I can run the man command with a C library function from the linux terminal?