1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html lang=en>
<head>
<title>tt.c</title>
</head>
<body>
<h1>tt.c</h1>
<p>tt.c -- tangle to, written by John Ankarström → <em>tt.c</em></p>
<pre><code>#include <stdio.h>
#ifdef _WIN32
#include <shlwapi.h>
#pragma comment(lib, "Shlwapi.lib")
#else
#include <ctype.h>
#include <errno.h>
#include <string.h>
#include <strings.h>
#include <stdlib.h>
#include <sys/stat.h>
#endif
<<definitions>>
#define err(code, string) do { fprintf(stderr, "%s: %s: %s\n", string, strerror(errno)); exit(code); } while (0)
#define die(...) do { fprintf(stderr, __VA_ARGS__); exit(1); } while (0)
#define true 1
#define false 0
#define bool int
<<declarations>>
int main(int argc, char *argv[]) {
<<main.declarations>>
<<main.globals>>
<<main.options>>
<<main.input>>
<<main.output>>
return 0;
}
void reference(char *line) {
<<reference.declarations>>
<<reference.parse>>
<<reference.add>>
}
bool insertion(char *line) {
<<insertion.declarations>>
<<insertion.parse>>
<<insertion.add>>
}
</code></pre>
<hr>
<h1>tt.input.c</h1>
<h2>References in source input</h2>
<p>The references found in the source input is stored as an array of strings
in the global refs variable: → <em>declarations</em></p>
<pre><code>char **refs; /* references */
int refs_c; /* count */
int refs_s; /* size (number of elements allocated for) */
</code></pre>
<p>It is allocated at the beginning of the execution to contain an array of
ten strings. The refs<em>s variable keeps track of the amount of allocated
space, while ref</em>c holds the number of actual elements: → <em>main.globals</em></p>
<pre><code> refs_c = 0;
refs_s = 10;
refs = malloc(refs_s * sizeof(char *));
if (refs == NULL) err(1, "malloc");
</code></pre>
<h2>Insertions in source input</h2>
<p>tt represents every insertion as an array of strings, where each string
corresponds to a line to be inserted. All insertions are stored in the
global ins array: → <em>declarations</em></p>
<pre><code>char ***ins; /* insertions */
</code></pre>
<p>The position of each insertion in the ins array is always equal to the
position of the corresponding reference in the refs array -- to find what
lines should be inserted at destination X, one must find the value P such
that refs[P] is equal to X. Then, the corresponding insertion will be equal
to ins[P].</p>
<p>In other words, the ins array should always be of the same length as refs.
As such, the refs<em>s and refs</em>c variables are used for ins as well. The ins
array is allocated to hold the same number of elements as refs. Furthermore,
its elements are set to NULL, signifying the absence of any insertion at
that index: → <em>main.globals</em></p>
<pre><code> ins = malloc(refs_s * sizeof(char **));
if (ins == NULL) err(1, "malloc");
for (i = 0; i < refs_s; i++)
ins[i] = NULL;
</code></pre>
<p>→ <em>main.declarations</em></p>
<pre><code>int i;
</code></pre>
<h2>Parsing standard input</h2>
<p>Text is read from the standard input, line by line, into a line variable.
Two additional variables, line<em>s and line</em>l, keep track of the amount of
allocated space and the actual number of characters in the string,
respectively: → <em>main.declarations</em></p>
<pre><code> char *line;
int line_l; /* length */
int line_s; /* size (number of characters allocated for) */
</code></pre>
<p>It initially is allocated to hold 100 characters: → <em>main.input</em></p>
<pre><code> line_l = 0;
line_s = 100;
line = malloc(1 + line_s * sizeof(char));
if (line == NULL) err(1, "malloc");
</code></pre>
<p>Lines are read character by character until end of file. First, the read
character is assigned to the variable b. When it is certain that it is not
EOF, then it is assigned to the variable c: → <em>main.input</em></p>
<pre><code> while ((b = getchar()) != EOF) {
c = b;
</code></pre>
<p>→ <em>main.declarations</em></p>
<pre><code> char b;
char c;
</code></pre>
<p>On every iteration, tt checks whether the read character is a newline. If
not, the character is added to the line variable, which is re-allocated if
necessary. The line_l, keeping track of the line's length, is incremented
as well: → <em>main.input</em></p>
<pre><code> if (c != '\n') {
if (line_l + 1 > line_s) {
line_s += 20;
tmp = realloc(line, 1 + line_s * sizeof(char));
if (tmp == NULL) err(1, "malloc");
line = tmp;
}
line[line_l++] = c;
continue;
}
</code></pre>
<p>The tmp variable used in the re-allocation has a type which is identical to
that of the line variable: → <em>main.declarations</em></p>
<pre><code> char *tmp;
</code></pre>
<p>If the read character is a newline, then the program "finishes" the line,
adding a final NULL character and resetting line_l: → <em>main.input</em></p>
<pre><code>finish:
line[line_l] = '\0';
line_l = 0;
</code></pre>
<p>Before parsing the line, we make sure to skip it if it is empty and
following a non-code line: → <em>main.input</em></p>
<pre><code> if (strlen(code_prefix) == 0 && !wascode && strcmp(line, "") == 0) {
continue;
}
</code></pre>
<p>This is only desirable if CODE_PREFIX is empty, because then, there is no
way for the writer of the source input to, for appearance's sake, leave an
empty line between non-code lines and code lines; any empty line will
will inevitably be interpreted as a code line. The code above circumvents
this.</p>
<p>This aesthetical nicety requires the program to keep track of whether the
previous line was a code line or not: → <em>main.declarations</em></p>
<pre><code> bool wascode = false;
</code></pre>
<p>Now, it is time to check whether the read line is a code line (an insertion)
or a documentation line (containing a reference): → <em>main.input</em></p>
<pre><code> if (!insertion(line)) reference(line);
}
</code></pre>
<p>The insertion and reference functions modify the ins and refs variables
according to the contents of the line.</p>
<p>Finally, after the loop is finished -- meaning that EOF has been reached --
we must ensure that the final character was not a newline; otherwise, the
final line of source input has not been processed, as lines are processed
only when the terminated newline is encountered.</p>
<p>Thus, if the final character was a newline, tt goes back and finishes the
final line: → <em>main.input</em></p>
<pre><code> if (c != '\n') { c = '\n'; goto finish; }
</code></pre>
<h2>Identifying and processing documentation lines containing references</h2>
<p>The reference function is responsible for processing references in source
input lines: → <em>declarations</em></p>
<pre><code>void reference(char *line);
</code></pre>
<h3>Parsing the line</h3>
<p>Documentation lines are formatted as follows: -></p>
<pre><code>documentation line ::= DOC_PREFIX anything [reference]
reference ::= "->" [whitespace] identifier [whitespace]
identifier ::= not whitespace
</code></pre>
<p>In order to identify whether a given line actually is a documentation line
containing a reference, the line variable is aliased to ln, which will be
modified instead of line: → <em>reference.declarations</em></p>
<pre><code> char *ln = line;
</code></pre>
<p>First, we ensure the line begins with the doc_prefix: → <em>reference.parse</em></p>
<pre><code> if (strncmp(ln, doc_prefix, strlen(doc_prefix)) != 0) return;
</code></pre>
<p>Then, we ensure that a hyphen is present: → <em>reference.parse</em></p>
<pre><code>hyphen:
if (*ln == '\0') return;
else if (*ln == '-') { ln++; goto lessthan; }
else { ln++; goto hyphen; }
</code></pre>
<p>After finding the hyphen, we check whether a less-then sign follows it.
If not, we keep looking for another hyphen. → <em>reference.parse</em></p>
<pre><code>lessthan:
if (*ln != '>') goto hyphen;
else ln++;
</code></pre>
<p>After finding a less-then sign following a hyphen (->), we ignore all
whitespace, if there is any. If the end of the line has been reached, or is
reached, by this point, then it will be interpreted as an empty reference,
resetting the current reference (meaning that subsequent code lines will not
be attached to any reference): → <em>reference.parse</em></p>
<pre><code>space:
if (isspace(*ln)) { ln++; goto space; }
if (*ln == '\0') { ref = ""; return; }
</code></pre>
<p>Now, a valid reference should be a string of non-space characters,
followed optionally by whitespace, but not anything other than whitespace:
→ <em>reference.parse</em></p>
<pre><code> for (i = 0; i < strlen(ln); i++)
if (isspace(ln[i])) {
for (j = i; j < strlen(ln); j++)
if (!isspace(ln[j])) return;
break;
}
</code></pre>
<p>→ <em>reference.declarations</em></p>
<pre><code> int i;
int j;
</code></pre>
<p>After the loop above, i will be set to the index of the first encountered
space or the end of the line. Any trailing whitespace should be ignored:
→ <em>reference.parse</em></p>
<pre><code> ln[i] = '\0';
</code></pre>
<h3>Adding the reference</h3>
<p>At this point, we have found a valid reference, which should now be added to
the global refs array.</p>
<p>First, however, it should be mentioned that reference identifiers have a
maximum length of 80 characters: → <em>definitions</em></p>
<pre><code>#define REFMAX 80
</code></pre>
<p>Thus, any reference identifier longer than REFMAX is truncated, with a
warning printed to the standard error stream: → <em>reference.add</em></p>
<pre><code> if (strlen(ln) > REFMAX) {
fprintf(stderr, "Warning: Truncating identifier exceeding %d characters\n",
REFMAX);
ln[REFMAX] = '\0';
}
</code></pre>
<p>It should also be mentioned that the current reference is always stored in a
global variable, from which the code(char <em>) function knows with which
reference to associate each code line: → </em>declarations*</p>
<pre><code>char *ref;
</code></pre>
<p>It is allocated in the beginning of the program's execution: → <em>main.globals</em></p>
<pre><code> ref = malloc(1 + REFMAX * sizeof(char));
if (ref == NULL) err(1, "malloc");
</code></pre>
<p>It is freed before the output section of the program, at which point it is
no longer needed: → <em>main.output</em></p>
<pre><code> free(ref);
</code></pre>
<p>The variable is set by our reference function: → <em>reference.add</em></p>
<pre><code> sprintf(ref, "%s", ln); /* set current reference */
ref[strlen(ln)] = '\0';
</code></pre>
<p>Now remains the work of adding the reference to the global refs variable --
unless it already exists in refs: → <em>reference.add</em></p>
<pre><code> for (i = 0; i < refs_c; i++)
if (strcmp(refs[i], ref) == 0) return;
</code></pre>
<p>If the reference truly is new, we notify the user: → <em>reference.add</em></p>
<pre><code> fprintf(stderr, "New reference: %s\n", ref);
</code></pre>
<p>Before adding the new reference to refs, we re-allocate refs (and therefore
also ins, which should always be as large as refs), if needed:
→ <em>reference.add</em></p>
<pre><code> if (++refs_c > refs_s) {
refs_s += 10;
tmp = realloc(refs, refs_s * sizeof(char *));
if (tmp == NULL) err(1, "malloc");
refs = tmp;
tmp2 = realloc(ins, refs_s * sizeof(char *));
if (tmp2 == NULL) err(1, "malloc");
ins = tmp2;
for (i = refs_s - 10; i < refs_s; i++) /* TODO: is this right? */
ins[i] = NULL;
}
</code></pre>
<p>→ <em>reference.declarations</em></p>
<pre><code> char **tmp;
char ***tmp2;
</code></pre>
<p>Notice that the code above also increases the refs_c count. Now, everything
else is done, and the reference is ready to be added: → <em>reference.add</em></p>
<pre><code> refs[refs_c-1] = malloc(1 + REFMAX * sizeof(char));
sprintf(refs[refs_c-1], "%s", ref);
</code></pre>
<h2>Identifying and processing code lines</h2>
<p>The insertion function is responsible for processing code lines:
→ <em>declarations</em></p>
<pre><code>bool insertion(char *line);
</code></pre>
<p>It returns true if the given line is a code line (i.e., an insertion).</p>
<h3>Parsing the code line</h3>
<p>First of all, if there is no current reference, the insertion should be
ignored: → <em>insertion.parse</em></p>
<pre><code> if (ref[0] == '\0') return false;
</code></pre>
<p>If there is a CODE<em>PREFIX, we ensure that the line begins with it.
Likewise, if there is a DOC</em>PREFIX, we ensure that the line does not
begin with it: → <em>insertion.parse</em></p>
<pre><code> if (strlen(code_prefix) > 0)
if (strncmp(line, code_prefix, strlen(code_prefix)) != 0) return false;
if (strlen(doc_prefix) > 0)
if (strncmp(line, doc_prefix, strlen(doc_prefix)) == 0) return false;
</code></pre>
<p>As you can see, the DOC<em>PREFIX is given precedence over the CODE</em>PREFIX.</p>
<h3>Adding the code line to the insertions</h3>
<p>Now that we know the line contains an insertion, we must find the index
of the current reference in the refs array: → <em>insertion.add</em></p>
<pre><code> for (i = 0; i < refs_c; i++)
if (strcmp(refs[i], ref) == 0) break;
</code></pre>
<p>→ <em>insertion.declarations</em></p>
<pre><code> int i;
</code></pre>
<p>Our goal is to add the insertion to the corresponding position in the ins
array. If there is no insertion at that position, the value will be NULL:
→ <em>insertion.add</em></p>
<pre><code> if (ins[i] == NULL) {
ins[i] = malloc(1 + 1 * sizeof(char *));
if (ins[i] == NULL) err(1, "malloc");
len = 0;
}
</code></pre>
<p>If ins[i] is not NULL, then it already contains some number of insertion
strings, terminated by a final NULL value. In order to allocate memory
for the new insertion, we find the position of the final NULL value,
corresponding to the length of the ins[i] array: → <em>insertion.add</em></p>
<pre><code> else {
for (len = 0; ins[i][len] != NULL; len++) ;
tmp = realloc(ins[i], 1 + (len + 1) * sizeof(char *));
if (tmp == NULL) err(1, "malloc");
ins[i] = tmp;
}
</code></pre>
<p>→ <em>insertion.declarations</em></p>
<pre><code> char **tmp;
int len;
</code></pre>
<p>Now remains adding the insertion to ins[i]. First, we mark the new final
position: → <em>insertion.add</em></p>
<pre><code> ins[i][len + 1] = NULL;
</code></pre>
<p>Then, we allocate memory for the string: → <em>insertion.add</em></p>
<pre><code> ins[i][len] = malloc(1 + strlen(line) * sizeof(char));
if (ins[i][len] == NULL) err(1, "malloc");
</code></pre>
<p>Finally, we copy the string, returning true, signifying that the line
processed indeed was a code line: → <em>insertion.add</em></p>
<pre><code> strncpy(ins[i][len], line + strlen(code_prefix),
strlen(line) - strlen(code_prefix));
ins[i][len][strlen(line) - strlen(code_prefix)] = '\0';
return true;
</code></pre>
<p>Notice also that we make sure to skip the CODE_PREFIX.</p>
<hr>
<h1>tt.options.c</h1>
<h2>Command-line flags</h2>
<p>tt can be configured by changing the value of three variables:
→ <em>declarations</em></p>
<pre><code>char *code_prefix; /* string with which code lines should start */
char *doc_prefix; /* string with which documentation lines should start */
char *out_prefix; /* string to which the output file name should be appended */
</code></pre>
<p>The default values are the following: → <em>main.options</em></p>
<pre><code> code_prefix = " "; /* code lines should begin with four spaces */
doc_prefix = ""; /* other lines are documentation lines */
out_prefix = "out/"; /* all output files go in the out/ directory */
</code></pre>
<p>Each variable is controlled by a single-letter command-line flag, which
should then be immediately -- without any space -- followed by the
desired value. For example, -dfinal. would set out_prefix to "final.".</p>
<p>This convention allows for a very simple parsing loop: → <em>main.options</em></p>
<pre><code> for (i = 1; i < argc; i++)
if (argv[i][0] == '-') {
switch(argv[i][1]) {
case 'c':
code_prefix = argv[i] + 2;
break;
case 'd':
doc_prefix = argv[i] + 2;
break;
case 'o':
out_prefix = argv[i] + 2;
break;
case '-':
i++;
goto end;
default:
die(USAGE);
}
} else
break;
end:
</code></pre>
<p>If the given argument begins with a hyphen, it is interpreted as a flag.
If the flag is --, then tt ignores the argument and stops looking for flags.
If the flag is unrecognized, the program dies. If the argument does not
begin with a hyphen, it and anything following it will not be interpreted
as a flag.</p>
<p>USAGE contains information about how to use tt: → <em>definitions</em></p>
<pre><code>#define USAGE "usage: %s [-cCODE_PREFIX] [-dDOC_PREFIX] [-oOUTPREFIX] destination ...\n", argv[0]
</code></pre>
<p>Of course, we can't just trust the user to provide reasonable values, so we
ensure that the code<em>prefix and out</em>prefix are not identical and that the
out_prefix is not empty -- otherwise, tt would overwrite all destination
files: → <em>main.options</em></p>
<pre><code> if (strcmp(code_prefix, doc_prefix) == 0)
die("code_prefix and doc_prefix cannot be identical\n");
if (strlen(out_prefix) == 0)
die("out_prefix cannot be empty\n");
</code></pre>
<h2>Command-line arguments</h2>
<p>Having finished parsing command-line flags, it is time to collect the
remaining command-line arguments, which should be one or more destination
files. Our loop above, when broken out of or finished naturally, has set
the i variable to the position of the first non-flag argument in argv (or
simply the position after the last flag in argv).</p>
<p>First, we check if there actually are any further argument, or if i is past
the end of the array: → <em>main.options</em></p>
<pre><code> if (i == argc) die(USAGE);
</code></pre>
<p>At least one destination file is required. Then, we save the position of the
first destination file in argv in a special variable for later use:
→ <em>main.options</em></p>
<pre><code>offset = i;
</code></pre>
<p>→ <em>main.declarations</em></p>
<pre><code>int offset;
</code></pre>
<p>Now, we have successfully finished parsing both flags and arguments, and are
ready to read the lines on the standard input.</p>
<hr>
<h1>tt.output.c</h1>
<h2>Outputting the results</h2>
<p>At this point, we have collected all references and accompanying insertinos
in the source input. Two tasks remain:</p>
<ol>
<li>We need to parse the destination files, identifying <<destinations>>.</li>
<li>We need to copy the destination files to the tangled files, overwriting
all <<destinations>> with the corresponding insertions.</li>
</ol>
<p>Both of these tasks will be performed in the same loop: → <em>main.output</em></p>
<pre><code> for (k = offset; k < argc; k++) {
</code></pre>
<p>→ <em>main.declarations</em></p>
<pre><code> int k;
</code></pre>
<p>The counter k is set to the offset defined in the options section, which
should be equal to the position of the first destination file in argv.
We loop as long as we haven't reached the end of argv.</p>
<p>On each iteration of the loop, we can obtain from argv the name of the
destination file and copy it to a new string, adding the out_prefix. We'll
call this string tangledfilename: → <em>main.declarations</em></p>
<pre><code> char *tangledfilename;
</code></pre>
<p>→ <em>main.output</em></p>
<pre><code> tangledfilename = malloc(1 + (strlen(out_prefix) + strlen(argv[k]) + 50) * sizeof(char));
if (tangledfilename == NULL) err(1, "malloc");
if (sprintf(tangledfilename, "%s%s", out_prefix, argv[k]) == -1)
err(1, "sprintf");
</code></pre>
<p>Now, we can open the tangled file for writing and the original destination
file for reading. We'll call the handle for tangledfile f and the handle for
argv[k] fo, the o standing for "original": → <em>main.declarations</em></p>
<pre><code> FILE *f;
FILE *fo;
</code></pre>
<p>→ <em>main.output</em></p>
<pre><code> f = fopen(tangledfilename, "w");
if (f == NULL) err(1, "fopen");
fo = fopen(argv[k], "r");
if (fo == NULL) err(1, "fopen");
</code></pre>
<p>Having successfully opened the files, we have no need for tangledfilename:
→ <em>main.output</em></p>
<pre><code> free(tangledfilename);
</code></pre>
<h3>Parsing the current destination file and writing the tangled file</h3>
<p>The destination file will be parsed in a manner similar to the way in which
the source input was parsed. The same structure will be used: → <em>main.output</em></p>
<pre><code> line = "";
line_l = 0;
/* line_s is remembered */
while ((b = fgetc(fo)) != EOF) {
c = b;
if (c != '\n') {
if (line_l + 1 > line_s) {
line_s += 20;
tmp = realloc(line, 1 + line_s * sizeof(char));
if (tmp == NULL) err(1, "malloc");
line = tmp;
}
line[line_l++] = c;
continue;
}
</code></pre>
<p>Again, characters will be added to the line variable until a newline is
encountered, at which point the collected line will be finished:
→ <em>main.output</em></p>
<pre><code>finish2:
line[line_l] = '\0';
line_l = 0; /* reset line length count */
</code></pre>
<p>From here on, however, the loop will look a bit different. First, tt takes
note of the line's indentation, saving it to the indent variable:
→ <em>main.declarations</em></p>
<pre><code> int indent;
</code></pre>
<p>Only spaces are currently supported: → <em>main.output</em></p>
<pre><code> ref = line;
for (indent = 0; *ref == ' '; ref++) indent++;
</code></pre>
<p>Also, as you can see, we re-use the ref variable that was used by the input
parsing, but which is now unused.</p>
<p>Parsing the <<destination identifier>> is simple: → <em>main.output</em></p>
<pre><code> if (strncmp(ref, "<<", 2) != 0
|| strncmp(ref + strlen(ref) - 2, ">>", 2) != 0) {
fprintf(f, "%s\n", line);
continue;
}
</code></pre>
<p>If no potential destination is found, then the line will be written as-is to
the tangled file, and the loop continues parsing the next line of the file.
If a potential destination is found, however, we store it in the ref
variable, removing the << and >> markers: → <em>main.output</em></p>
<pre><code> ref += 2;
ref[strlen(ref) - 2] = '\0';
</code></pre>
<p>There is still one thing to check, before we know that the destination is
valid -- it must not contain any whitespace: → <em>main.output</em></p>
<pre><code> for (i = 0; i < strlen(ref); i++)
if (isspace(ref[i])) {
fprintf(f, "%s\n", line);
continue;
}
</code></pre>
<p>Again, if there is whitespace, then the line does not signify a destination
and should be printed as-is to the resulting tangled file.</p>
<p>As when parsing the input, long identifiers are truncated: → <em>main.output</em></p>
<pre><code> if (strlen(ref) > REFMAX)
fprintf(stderr,
"Warning: Truncating identifier exceeding %d characters\n", REFMAX);
</code></pre>
<p>Finally, we check whether the destination actually has been referenced by
the source input, warning the user otherwise: → <em>main.output</em></p>
<pre><code> for (i = 0; i < refs_c; i++)
if (strncmp(refs[i], ref, REFMAX) == 0) goto found;
fprintf(stderr, "Unreferenced destination: %s\n", ref);
continue;
found:
</code></pre>
<p>Having established that the identified destination is referenced by the
source input, and having stored in the local i variable the reference's
position in the refs variable, we can retrieve the insertion for the
reference by looking at the same position in the ins variable.</p>
<p>Our first order of business is to make sure that the insertion is not empty
-- in that case, the user is warned, and the loop goes on to the next line:
→ <em>main.output</em></p>
<pre><code> if (ins[i] == NULL) {
fprintf(stderr, "Warning: Insertion for %s is empty\n", ref);
continue;
}
</code></pre>
<p>Now, we are ready to write the insertion for the destination to the tangled
file. Because each insertion is stored as an array of strings, each string
containing a single line of the insertion, we use yet another loop:
→ <em>main.output</em></p>
<pre><code> for (j = 0; ins[i][j] != NULL; j++) {
if (ins[i][j + 1] == NULL) {
if (strlen(ins[i][j]) == 0)
break; /* remove extra newline */
}
for (m = indent; m > 0; m--) putc(' ', f);
fprintf(f, "%s\n", ins[i][j]);
}
}
</code></pre>
<p>→ <em>main.declarations</em></p>
<pre><code>int j;
int m;
</code></pre>
<p>Apart from simply printing the inserted line to the tangled file, the code
above also skips any empty line at the end of the insertion and adds the
indentation identified when parsing the line in the destination file
containing the destination identifier.</p>
<p>Now, we have almost finished parsing the current destination file and
writing to the corresponding tangled file, but -- as before -- we still
haven't processed the final line of the file, if that line ends without
a newline. To fix that, we just run the finishing code again:
→ <em>main.output</em></p>
<pre><code> if (c != '\n') { c = '\n'; goto finish2; }
</code></pre>
<p>Finally, we close the handles to the destination file and tangled file:
→ <em>main.output</em></p>
<pre><code> fclose(f);
fclose(fo);
}
</code></pre>
<p>And that is the end of the loop. The loop continues for every destination
file given as an argument, and when it is done, so is the program.</p>
<hr>
</body></html>
|