html.c

// https://old.reddit.com/r/C_Programming/comments/1l1hxeu
#include <assert.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define S(s)    (Str){s, sizeof(s)-1}

typedef struct {
    char     *data;
    ptrdiff_t len;
} Str;

static _Bool equals(Str a, Str b)
{
    if (a.len != b.len) {
        return 0;
    }
    return !a.len || !memcmp(a.data, b.data, a.len);
}

static Str slice(Str s, ptrdiff_t beg, ptrdiff_t end)
{
    assert(beg>=0 && beg<=end);
    return (Str){s.data+beg, end-beg};
}

static _Bool whitespace(char c)
{
    return c==' ' || c=='\t' || c=='\n' || c=='\r';
}

static Str lstrip(Str s)
{
    for (; s.len && whitespace(*s.data); s = slice(s, 1, s.len)) {}
    return s;
}

static Str readfile(FILE *f)
{
    Str r = {0};
    for (;;) {
        int   grow = 1<<14;  // amount to read at a time
        void *new  = realloc(r.data, r.len+grow);
        if (!new) {
            return r;  // TODO: handle allocation failure
        }
        r.data = new;

        ptrdiff_t n = fread(r.data+r.len, 1, grow, f);
        r.len += n;
        if (n < grow) {
            return r;  // TODO: ferror() to check read error
        }
    }
}

typedef struct {
    Str token;
    Str tail;
} Result;

static _Bool special(char c)
{
    return whitespace(c) || c=='"' || c=='<' || c=='>' || c=='"' || c=='=';
}

static Result tokenize(Str s)
{
    Result r = {0};

    s = lstrip(s);
    if (!s.len) {
        return r;  // done
    }

    ptrdiff_t toklen = 1;
    switch (*s.data) {
    case '<':
        if (s.len > 1) {
            switch (s.data[1]) {
            case '!':
            case '/': toklen = 2;
                      break;
            }
        }
        break;

    case '>':
    case '"':
        break;

    default:
        for (; toklen<s.len && !special(s.data[toklen]); toklen++) {}
    }

    r.token = slice(s,      0, toklen);
    r.tail  = slice(s, toklen,  s.len);
    return r;
}

int main(void)
{
    Result r = {0};
    r.tail = readfile(stdin);

    for (;;) {
        r = tokenize(r.tail);
        if (!r.token.len) break;
        if (!equals(r.token, S("class"))) {
            continue;
        }

        r = tokenize(r.tail);
        if (!r.token.len) break;
        if (!equals(r.token, S("="))) {
            continue;
        }

        r = tokenize(r.tail);
        if (!r.token.len) break;
        if (!equals(r.token, S("\""))) {
            continue;
        }

        for (;;) {
            r = tokenize(r.tail);
            if (!r.token.len || equals(r.token, S("\""))) break;
            fwrite(r.token.data, 1, r.token.len, stdout);
            putchar('\n');
        }
    }

    fflush(stdout);
    return ferror(stdout);
}