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markdown.c
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markdown.c
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/*
a little program to convert markdown to html, for READMEs
I was using markdown.pl but that has some annoying problems
This doesn't support all of markdown; I'll add more as I need it.
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
/* output text with *s for italics and stuff */
static void output_md_text(FILE *out, int *flags, int line_number, const char *text) {
enum {
FLAG_I = 0x01, /* italics */
FLAG_B = 0x02,
FLAG_CODE = 0x04
};
const char *p;
for (p = text; *p; ++p) {
if ((*flags & FLAG_CODE) && *p != '`') {
switch (*p) {
case '<': fprintf(out, "<"); break;
case '>': fprintf(out, ">"); break;
case '&': fprintf(out, "&"); break;
default: putc(*p, out); break;
}
continue;
}
switch (*p) {
case '\\':
++p;
if (*p == '\0') {
fprintf(stderr, "line %d: Unterminated \\.\n", line_number);
exit(-1);
}
fprintf(out, "%c", *p);
break;
case '*':
if (p[1] == '*') {
/* bold */
if (*flags & FLAG_B) {
fprintf(out, "</b>");
*flags &= ~FLAG_B;
} else {
fprintf(out, "<b>");
*flags |= FLAG_B;
}
++p;
} else {
/* italics */
if (*flags & FLAG_I) {
fprintf(out, "</i>");
*flags &= ~FLAG_I;
} else {
fprintf(out, "<i>");
*flags |= FLAG_I;
}
}
break;
case '`':
/* code */
if (*flags & FLAG_CODE) {
fprintf(out, "</code>");
*flags &= ~FLAG_CODE;
} else {
fprintf(out, "<code>");
*flags |= FLAG_CODE;
}
break;
case '[': {
/* link */
char url2[256] = {0};
const char *label, *url, *label_end, *url_end;
char *dot;
int n_label, n_url;
label = p+1;
label_end = strchr(label, ']');
if (!label_end) {
fprintf(stderr, "line %d: Unterminated link.\n", line_number);
exit(-1);
}
if (label_end[1] != '(') {
fprintf(stderr, "line %d: Bad link syntax.\n", line_number);
exit(-1);
}
url = label_end + 2;
url_end = strchr(url, ')');
if (!url_end) {
fprintf(stderr, "line %d: Unterminated URL.\n", line_number);
exit(-1);
}
n_label = (int)(label_end - label);
n_url = (int)(url_end - url);
if (n_url > sizeof url2-8)
n_url = sizeof url2-8;
sprintf(url2, "%.*s", n_url, url);
dot = strrchr(url2, '.');
if (dot && strcmp(dot, ".md") == 0) {
/* replace links to md files with links to html files */
strcpy(dot, ".html");
}
fprintf(out, "<a href=\"%s\">%.*s</a>",
url2, n_label, label);
p = url_end;
} break;
case '-':
if (p[1] == '-') {
/* em dash */
fprintf(out, "—");
++p;
} else {
goto default_case;
}
break;
default:
default_case:
putc(*p, out);
break;
}
}
}
int main(int argc, char **argv) {
FILE *in, *out;
char line[1024] = {0};
char title[256] = {0};
int flags = 0, txtflags = 0;
int line_number = 0;
enum {
FLAG_UL = 1
};
if (argc < 2) {
fprintf(stderr, "Please provide an input file.\n");
return -1;
}
{
const char *in_filename = argv[1];
char out_filename[256] = {0};
char *dot;
strncpy(out_filename, argv[1], 200);
dot = strrchr(out_filename, '.');
if (!dot || strcmp(dot, ".md") != 0) {
fprintf(stderr, "Input filename does not end in .md\n");
return -1;
}
*dot = '\0';
strcpy(title, out_filename);
strcpy(dot, ".html");
in = fopen(in_filename, "rb");
out = fopen(out_filename, "wb");
}
if (!in) {
perror("Couldn't open input file");
return -1;
}
if (!out) {
perror("Couldn't open output file");
return -1;
}
fprintf(out,
"<!DOCTYPE html>\n"
"<html lang=\"en\">\n"
"<head>\n"
"<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">\n"
"<meta charset=\"utf-8\">\n"
"<style>\n"
"body { font-family: serif; }\n"
"</style>\n"
"<title>%s</title>\n"
"</head>\n"
"<body>\n"
"<p>\n", title
);
while (fgets(line, sizeof line, in)) {
++line_number;
line[strcspn(line, "\r\n")] = '\0';
if (line[0] == '#') {
/* heading */
int n = 1;
while (line[n] == '#') ++n;
fprintf(out, "</p><h%d>", n);
output_md_text(out, &txtflags, line_number, line + n);
fprintf(out, "</h%d><p>\n", n);
} else if (line[0] == '\0') {
if (flags & FLAG_UL) {
fprintf(out, "</li></ul>\n");
flags &= ~FLAG_UL;
}
fprintf(out, "</p>\n<p>\n");
} else if (strncmp(line, "- ", 2) == 0) {
/* bullet */
if (flags & FLAG_UL) {
fprintf(out, "</li><li>");
} else {
fprintf(out, "<ul><li>");
flags |= FLAG_UL;
}
output_md_text(out, &txtflags, line_number, line + 2);
fprintf(out, "\n");
} else if (strncmp(line, "```", 3) == 0) {
fprintf(out, "<pre><code>\n");
while (fgets(line, sizeof line, in)) {
char *p;
++line_number;
if (strncmp(line, "```", 3) == 0)
break;
for (p = line; *p; ++p) {
switch (*p) {
case '<': fprintf(out, "<"); break;
case '>': fprintf(out, ">"); break;
case '&': fprintf(out, "&"); break;
default: fputc(*p, out); break;
}
}
}
fprintf(out, "</code></pre>\n");
} else {
output_md_text(out, &txtflags, line_number, line);
fprintf(out, "\n");
}
}
fprintf(out, "</p>\n</body>\n</html>\n");
return 0;
}