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
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
|
<HTML>
<HEAD>
<!-- This HTML file has been created by texi2html 1.52a
from gettext.texi on 24 April 2002 -->
<TITLE>GNU gettext utilities - 3 Preparing Program Sources</TITLE>
</HEAD>
<BODY>
Go to the <A HREF="gettext_1.html">first</A>, <A HREF="gettext_2.html">previous</A>, <A HREF="gettext_4.html">next</A>, <A HREF="gettext_22.html">last</A> section, <A HREF="gettext_toc.html">table of contents</A>.
<P><HR><P>
<H1><A NAME="SEC13" HREF="gettext_toc.html#TOC13">3 Preparing Program Sources</A></H1>
<P>
<A NAME="IDX111"></A>
</P>
<P>
For the programmer, changes to the C source code fall into three
categories. First, you have to make the localization functions
known to all modules needing message translation. Second, you should
properly trigger the operation of GNU <CODE>gettext</CODE> when the program
initializes, usually from the <CODE>main</CODE> function. Last, you should
identify and especially mark all constant strings in your program
needing translation.
</P>
<P>
Presuming that your set of programs, or package, has been adjusted
so all needed GNU <CODE>gettext</CODE> files are available, and your
<TT>`Makefile´</TT> files are adjusted (see section <A HREF="gettext_12.html#SEC172">12 The Maintainer's View</A>), each C module
having translated C strings should contain the line:
</P>
<P>
<A NAME="IDX112"></A>
<PRE>
#include <libintl.h>
</PRE>
<P>
The remaining changes to your C sources are discussed in the further
sections of this chapter.
</P>
<H2><A NAME="SEC14" HREF="gettext_toc.html#TOC14">3.1 Triggering <CODE>gettext</CODE> Operations</A></H2>
<P>
<A NAME="IDX113"></A>
The initialization of locale data should be done with more or less
the same code in every program, as demonstrated below:
</P>
<PRE>
int
main (argc, argv)
int argc;
char argv;
{
...
setlocale (LC_ALL, "");
bindtextdomain (PACKAGE, LOCALEDIR);
textdomain (PACKAGE);
...
}
</PRE>
<P>
<VAR>PACKAGE</VAR> and <VAR>LOCALEDIR</VAR> should be provided either by
<TT>`config.h´</TT> or by the Makefile. For now consult the <CODE>gettext</CODE>
or <CODE>hello</CODE> sources for more information.
</P>
<P>
<A NAME="IDX114"></A>
<A NAME="IDX115"></A>
The use of <CODE>LC_ALL</CODE> might not be appropriate for you.
<CODE>LC_ALL</CODE> includes all locale categories and especially
<CODE>LC_CTYPE</CODE>. This later category is responsible for determining
character classes with the <CODE>isalnum</CODE> etc. functions from
<TT>`ctype.h´</TT> which could especially for programs, which process some
kind of input language, be wrong. For example this would mean that a
source code using the ç (c-cedilla character) is runnable in
France but not in the U.S.
</P>
<P>
Some systems also have problems with parsing numbers using the
<CODE>scanf</CODE> functions if an other but the <CODE>LC_ALL</CODE> locale is used.
The standards say that additional formats but the one known in the
<CODE>"C"</CODE> locale might be recognized. But some systems seem to reject
numbers in the <CODE>"C"</CODE> locale format. In some situation, it might
also be a problem with the notation itself which makes it impossible to
recognize whether the number is in the <CODE>"C"</CODE> locale or the local
format. This can happen if thousands separator characters are used.
Some locales define this character accordfing to the national
conventions to <CODE>'.'</CODE> which is the same character used in the
<CODE>"C"</CODE> locale to denote the decimal point.
</P>
<P>
So it is sometimes necessary to replace the <CODE>LC_ALL</CODE> line in the
code above by a sequence of <CODE>setlocale</CODE> lines
</P>
<PRE>
{
...
setlocale (LC_CTYPE, "");
setlocale (LC_MESSAGES, "");
...
}
</PRE>
<P>
<A NAME="IDX116"></A>
<A NAME="IDX117"></A>
<A NAME="IDX118"></A>
<A NAME="IDX119"></A>
<A NAME="IDX120"></A>
<A NAME="IDX121"></A>
<A NAME="IDX122"></A>
On all POSIX conformant systems the locale categories <CODE>LC_CTYPE</CODE>,
<CODE>LC_COLLATE</CODE>, <CODE>LC_MONETARY</CODE>, <CODE>LC_NUMERIC</CODE>, and
<CODE>LC_TIME</CODE> are available. On some modern systems there is also a
locale <CODE>LC_MESSAGES</CODE> which is called on some old, XPG2 compliant
systems <CODE>LC_RESPONSES</CODE>.
</P>
<P>
Note that changing the <CODE>LC_CTYPE</CODE> also affects the functions
declared in the <CODE><ctype.h></CODE> standard header. If this is not
desirable in your application (for example in a compiler's parser),
you can use a set of substitute functions which hardwire the C locale,
such as found in the <CODE><c-ctype.h></CODE> and <CODE><c-ctype.c></CODE> files
in the gettext source distribution.
</P>
<P>
It is also possible to switch the locale forth and back between the
environment dependent locale and the C locale, but this approach is
normally avoided because a <CODE>setlocale</CODE> call is expensive,
because it is tedious to determine the places where a locale switch
is needed in a large program's source, and because switching a locale
is not multithread-safe.
</P>
<H2><A NAME="SEC15" HREF="gettext_toc.html#TOC15">3.2 Preparing Translatable Strings</A></H2>
<P>
<A NAME="IDX123"></A>
Before strings can be marked for translations, they sometimes need to
be adjusted. Usually preparing a string for translation is done right
before marking it, during the marking phase which is described in the
next sections. What you have to keep in mind while doing that is the
following.
</P>
<UL>
<LI>
Decent English style.
<LI>
Entire sentences.
<LI>
Split at paragraphs.
<LI>
Use format strings instead of string concatenation.
</UL>
<P>
Let's look at some examples of these guidelines.
</P>
<P>
<A NAME="IDX124"></A>
Translatable strings should be in good English style. If slang language
with abbreviations and shortcuts is used, often translators will not
understand the message and will produce very inappropriate translations.
</P>
<PRE>
"%s: is parameter\n"
</PRE>
<P>
This is nearly untranslatable: Is the displayed item <EM>a</EM> parameter or
<EM>the</EM> parameter?
</P>
<PRE>
"No match"
</PRE>
<P>
The ambiguity in this message makes it ununderstandable: Is the program
attempting to set something on fire? Does it mean "The given object does
not match the template"? Does it mean "The template does not fit for any
of the objects"?
</P>
<P>
<A NAME="IDX125"></A>
In both cases, adding more words to the message will help both the
translator and the English speaking user.
</P>
<P>
<A NAME="IDX126"></A>
Translatable strings should be entire sentences. It is often not possible
to translate single verbs or adjectives in a substitutable way.
</P>
<PRE>
printf ("File %s is %s protected", filename, rw ? "write" : "read");
</PRE>
<P>
Most translators will not look at the source and will thus only see the
string <CODE>"File %s is %s protected"</CODE>, which is unintelligible. Change
this to
</P>
<PRE>
printf (rw ? "File %s is write protected" : "File %s is read protected",
filename);
</PRE>
<P>
This way the translator will not only understand the message, she will
also be able to find the appropriate grammatical construction. The French
translator for example translates "write protected" like "protected
against writing".
</P>
<P>
Often sentences don't fit into a single line. If a sentence is output
using two subsequent <CODE>printf</CODE> statements, like this
</P>
<PRE>
printf ("Locale charset \"%s\" is different from\n", lcharset);
printf ("input file charset \"%s\".\n", fcharset);
</PRE>
<P>
the translator would have to translate two half sentences, but nothing
in the POT file would tell her that the two half sentences belong together.
It is necessary to merge the two <CODE>printf</CODE> statements so that the
translator can handle the entire sentence at once and decide at which
place to insert a line break in the translation (if at all):
</P>
<PRE>
printf ("Locale charset \"%s\" is different from\n\
input file charset \"%s\".\n", lcharset, fcharset);
</PRE>
<P>
You may now ask: how about two or more adjacent sentences? Like in this case:
</P>
<PRE>
puts ("Apollo 13 scenario: Stack overflow handling failed.");
puts ("On the next stack overflow we will crash!!!");
</PRE>
<P>
Should these two statements merged into a single one? I would recommend to
merge them if the two sentences are related to each other, because then it
makes it easier for the translator to understand and translate both. On
the other hand, if one of the two messages is a stereotypic one, occurring
in other places as well, you will do a favour to the translator by not
merging the two. (Identical messages occurring in several places are
combined by xgettext, so the translator has to handle them once only.)
</P>
<P>
<A NAME="IDX127"></A>
Translatable strings should be limited to one paragraph; don't let a
single message be longer than ten lines. The reason is that when the
translatable string changes, the translator is faced with the task of
updating the entire translated string. Maybe only a single word will
have changed in the English string, but the translator doesn't see that
(with the current translation tools), therefore she has to proofread
the entire message.
</P>
<P>
<A NAME="IDX128"></A>
Many GNU programs have a <SAMP>`--help´</SAMP> output that extends over several
screen pages. It is a courtesy towards the translators to split such a
message into several ones of five to ten lines each. While doing that,
you can also attempt to split the documented options into groups,
such as the input options, the output options, and the informative
output options. This will help every user to find the option he is
looking for.
</P>
<P>
<A NAME="IDX129"></A>
<A NAME="IDX130"></A>
Hardcoded string concatenation is sometimes used to construct English
strings:
</P>
<PRE>
strcpy (s, "Replace ");
strcat (s, object1);
strcat (s, " with ");
strcat (s, object2);
strcat (s, "?");
</PRE>
<P>
In order to present to the translator only entire sentences, and also
because in some languages the translator might want to swap the order
of <CODE>object1</CODE> and <CODE>object2</CODE>, it is necessary to change this
to use a format string:
</P>
<PRE>
sprintf (s, "Replace %s with %s?", object1, object2);
</PRE>
<P>
<A NAME="IDX131"></A>
A similar case is compile time concatenation of strings. The ISO C 99
include file <CODE><inttypes.h></CODE> contains a macro <CODE>PRId64</CODE> that
can be used as a formatting directive for outputting an <SAMP>`int64_t´</SAMP>
integer through <CODE>printf</CODE>. It expands to a constant string, usually
"d" or "ld" or "lld" or something like this, depending on the platform.
Assume you have code like
</P>
<PRE>
printf ("The amount is %0" PRId64 "\n"), number);
</PRE>
<P>
After marking, this cannot become
</P>
<PRE>
printf (gettext ("The amount is %0") PRId64 "\n"), number);
</PRE>
<P>
because it would simply be invalid C syntax. It cannot become
</P>
<PRE>
printf (gettext ("The amount is %0" PRId64 "\n")), number);
</PRE>
<P>
because the value of <CODE>PRId64</CODE> is not known to <CODE>xgettext</CODE>, and
even if were, there would be three or more possibilities, and the
translator would have to translate three or more strings that differ in
a single letter.
</P>
<P>
The solution for this problem is to change the code like this:
</P>
<PRE>
char buf1[100];
sprintf (buf1, "%0" PRId64, number);
printf (gettext ("The amount is %s\n"), buf1);
</PRE>
<P>
This means, you put the platform dependent code in one statement, and the
internationalization code in a different statement. Note that a buffer length
of 100 is safe, because all available hardware integer types are limited to
128 bits, and to print a 128 bit integer one needs at most 54 characters,
regardless whether in decimal, octal or hexadecimal.
</P>
<P>
<A NAME="IDX132"></A>
All this applies to other programming languages as well. For example, in
Java, string contenation is very frequently used, because it is a compiler
built-in operator. Like in C, in Java, you would change
</P>
<PRE>
System.out.println("Replace "+object1+" with "+object2+"?");
</PRE>
<P>
into a statement involving a format string:
</P>
<PRE>
System.out.println(
MessageFormat.format("Replace {0} with {1}?",
new Object[] { object1, object2 }));
</PRE>
<H2><A NAME="SEC16" HREF="gettext_toc.html#TOC16">3.3 How Marks Appear in Sources</A></H2>
<P>
<A NAME="IDX133"></A>
</P>
<P>
All strings requiring translation should be marked in the C sources. Marking
is done in such a way that each translatable string appears to be
the sole argument of some function or preprocessor macro. There are
only a few such possible functions or macros meant for translation,
and their names are said to be marking keywords. The marking is
attached to strings themselves, rather than to what we do with them.
This approach has more uses. A blatant example is an error message
produced by formatting. The format string needs translation, as
well as some strings inserted through some <SAMP>`%s´</SAMP> specification
in the format, while the result from <CODE>sprintf</CODE> may have so many
different instances that it is impractical to list them all in some
<SAMP>`error_string_out()´</SAMP> routine, say.
</P>
<P>
This marking operation has two goals. The first goal of marking
is for triggering the retrieval of the translation, at run time.
The keyword are possibly resolved into a routine able to dynamically
return the proper translation, as far as possible or wanted, for the
argument string. Most localizable strings are found in executable
positions, that is, attached to variables or given as parameters to
functions. But this is not universal usage, and some translatable
strings appear in structured initializations. See section <A HREF="gettext_3.html#SEC19">3.6 Special Cases of Translatable Strings</A>.
</P>
<P>
The second goal of the marking operation is to help <CODE>xgettext</CODE>
at properly extracting all translatable strings when it scans a set
of program sources and produces PO file templates.
</P>
<P>
The canonical keyword for marking translatable strings is
<SAMP>`gettext´</SAMP>, it gave its name to the whole GNU <CODE>gettext</CODE>
package. For packages making only light use of the <SAMP>`gettext´</SAMP>
keyword, macro or function, it is easily used <EM>as is</EM>. However,
for packages using the <CODE>gettext</CODE> interface more heavily, it
is usually more convenient to give the main keyword a shorter, less
obtrusive name. Indeed, the keyword might appear on a lot of strings
all over the package, and programmers usually do not want nor need
their program sources to remind them forcefully, all the time, that they
are internationalized. Further, a long keyword has the disadvantage
of using more horizontal space, forcing more indentation work on
sources for those trying to keep them within 79 or 80 columns.
</P>
<P>
<A NAME="IDX134"></A>
Many packages use <SAMP>`_´</SAMP> (a simple underline) as a keyword,
and write <SAMP>`_("Translatable string")´</SAMP> instead of <SAMP>`gettext
("Translatable string")´</SAMP>. Further, the coding rule, from GNU standards,
wanting that there is a space between the keyword and the opening
parenthesis is relaxed, in practice, for this particular usage.
So, the textual overhead per translatable string is reduced to
only three characters: the underline and the two parentheses.
However, even if GNU <CODE>gettext</CODE> uses this convention internally,
it does not offer it officially. The real, genuine keyword is truly
<SAMP>`gettext´</SAMP> indeed. It is fairly easy for those wanting to use
<SAMP>`_´</SAMP> instead of <SAMP>`gettext´</SAMP> to declare:
</P>
<PRE>
#include <libintl.h>
#define _(String) gettext (String)
</PRE>
<P>
instead of merely using <SAMP>`#include <libintl.h>´</SAMP>.
</P>
<P>
Later on, the maintenance is relatively easy. If, as a programmer,
you add or modify a string, you will have to ask yourself if the
new or altered string requires translation, and include it within
<SAMP>`_()´</SAMP> if you think it should be translated. <SAMP>`"%s: %d"´</SAMP> is
an example of string <EM>not</EM> requiring translation!
</P>
<H2><A NAME="SEC17" HREF="gettext_toc.html#TOC17">3.4 Marking Translatable Strings</A></H2>
<P>
<A NAME="IDX135"></A>
</P>
<P>
In PO mode, one set of features is meant more for the programmer than
for the translator, and allows him to interactively mark which strings,
in a set of program sources, are translatable, and which are not.
Even if it is a fairly easy job for a programmer to find and mark
such strings by other means, using any editor of his choice, PO mode
makes this work more comfortable. Further, this gives translators
who feel a little like programmers, or programmers who feel a little
like translators, a tool letting them work at marking translatable
strings in the program sources, while simultaneously producing a set of
translation in some language, for the package being internationalized.
</P>
<P>
<A NAME="IDX136"></A>
The set of program sources, targetted by the PO mode commands describe
here, should have an Emacs tags table constructed for your project,
prior to using these PO file commands. This is easy to do. In any
shell window, change the directory to the root of your project, then
execute a command resembling:
</P>
<PRE>
etags src/*.[hc] lib/*.[hc]
</PRE>
<P>
presuming here you want to process all <TT>`.h´</TT> and <TT>`.c´</TT> files
from the <TT>`src/´</TT> and <TT>`lib/´</TT> directories. This command will
explore all said files and create a <TT>`TAGS´</TT> file in your root
directory, somewhat summarizing the contents using a special file
format Emacs can understand.
</P>
<P>
<A NAME="IDX137"></A>
For packages following the GNU coding standards, there is
a make goal <CODE>tags</CODE> or <CODE>TAGS</CODE> which constructs the tag files in
all directories and for all files containing source code.
</P>
<P>
Once your <TT>`TAGS´</TT> file is ready, the following commands assist
the programmer at marking translatable strings in his set of sources.
But these commands are necessarily driven from within a PO file
window, and it is likely that you do not even have such a PO file yet.
This is not a problem at all, as you may safely open a new, empty PO
file, mainly for using these commands. This empty PO file will slowly
fill in while you mark strings as translatable in your program sources.
</P>
<DL COMPACT>
<DT><KBD>,</KBD>
<DD>
<A NAME="IDX138"></A>
Search through program sources for a string which looks like a
candidate for translation (<CODE>po-tags-search</CODE>).
<DT><KBD>M-,</KBD>
<DD>
<A NAME="IDX139"></A>
Mark the last string found with <SAMP>`_()´</SAMP> (<CODE>po-mark-translatable</CODE>).
<DT><KBD>M-.</KBD>
<DD>
<A NAME="IDX140"></A>
Mark the last string found with a keyword taken from a set of possible
keywords. This command with a prefix allows some management of these
keywords (<CODE>po-select-mark-and-mark</CODE>).
</DL>
<P>
<A NAME="IDX141"></A>
The <KBD>,</KBD> (<CODE>po-tags-search</CODE>) command searches for the next
occurrence of a string which looks like a possible candidate for
translation, and displays the program source in another Emacs window,
positioned in such a way that the string is near the top of this other
window. If the string is too big to fit whole in this window, it is
positioned so only its end is shown. In any case, the cursor
is left in the PO file window. If the shown string would be better
presented differently in different native languages, you may mark it
using <KBD>M-,</KBD> or <KBD>M-.</KBD>. Otherwise, you might rather ignore it
and skip to the next string by merely repeating the <KBD>,</KBD> command.
</P>
<P>
A string is a good candidate for translation if it contains a sequence
of three or more letters. A string containing at most two letters in
a row will be considered as a candidate if it has more letters than
non-letters. The command disregards strings containing no letters,
or isolated letters only. It also disregards strings within comments,
or strings already marked with some keyword PO mode knows (see below).
</P>
<P>
If you have never told Emacs about some <TT>`TAGS´</TT> file to use, the
command will request that you specify one from the minibuffer, the
first time you use the command. You may later change your <TT>`TAGS´</TT>
file by using the regular Emacs command <KBD>M-x visit-tags-table</KBD>,
which will ask you to name the precise <TT>`TAGS´</TT> file you want
to use. See section `Tag Tables' in <CITE>The Emacs Editor</CITE>.
</P>
<P>
Each time you use the <KBD>,</KBD> command, the search resumes from where it was
left by the previous search, and goes through all program sources,
obeying the <TT>`TAGS´</TT> file, until all sources have been processed.
However, by giving a prefix argument to the command (<KBD>C-u
,)</KBD>, you may request that the search be restarted all over again
from the first program source; but in this case, strings that you
recently marked as translatable will be automatically skipped.
</P>
<P>
Using this <KBD>,</KBD> command does not prevent using of other regular
Emacs tags commands. For example, regular <CODE>tags-search</CODE> or
<CODE>tags-query-replace</CODE> commands may be used without disrupting the
independent <KBD>,</KBD> search sequence. However, as implemented, the
<EM>initial</EM> <KBD>,</KBD> command (or the <KBD>,</KBD> command is used with a
prefix) might also reinitialize the regular Emacs tags searching to the
first tags file, this reinitialization might be considered spurious.
</P>
<P>
<A NAME="IDX142"></A>
<A NAME="IDX143"></A>
The <KBD>M-,</KBD> (<CODE>po-mark-translatable</CODE>) command will mark the
recently found string with the <SAMP>`_´</SAMP> keyword. The <KBD>M-.</KBD>
(<CODE>po-select-mark-and-mark</CODE>) command will request that you type
one keyword from the minibuffer and use that keyword for marking
the string. Both commands will automatically create a new PO file
untranslated entry for the string being marked, and make it the
current entry (making it easy for you to immediately proceed to its
translation, if you feel like doing it right away). It is possible
that the modifications made to the program source by <KBD>M-,</KBD> or
<KBD>M-.</KBD> render some source line longer than 80 columns, forcing you
to break and re-indent this line differently. You may use the <KBD>O</KBD>
command from PO mode, or any other window changing command from
Emacs, to break out into the program source window, and do any
needed adjustments. You will have to use some regular Emacs command
to return the cursor to the PO file window, if you want command
<KBD>,</KBD> for the next string, say.
</P>
<P>
The <KBD>M-.</KBD> command has a few built-in speedups, so you do not
have to explicitly type all keywords all the time. The first such
speedup is that you are presented with a <EM>preferred</EM> keyword,
which you may accept by merely typing <KBD><KBD>RET</KBD></KBD> at the prompt.
The second speedup is that you may type any non-ambiguous prefix of the
keyword you really mean, and the command will complete it automatically
for you. This also means that PO mode has to <EM>know</EM> all
your possible keywords, and that it will not accept mistyped keywords.
</P>
<P>
If you reply <KBD>?</KBD> to the keyword request, the command gives a
list of all known keywords, from which you may choose. When the
command is prefixed by an argument (<KBD>C-u M-.</KBD>), it inhibits
updating any program source or PO file buffer, and does some simple
keyword management instead. In this case, the command asks for a
keyword, written in full, which becomes a new allowed keyword for
later <KBD>M-.</KBD> commands. Moreover, this new keyword automatically
becomes the <EM>preferred</EM> keyword for later commands. By typing
an already known keyword in response to <KBD>C-u M-.</KBD>, one merely
changes the <EM>preferred</EM> keyword and does nothing more.
</P>
<P>
All keywords known for <KBD>M-.</KBD> are recognized by the <KBD>,</KBD> command
when scanning for strings, and strings already marked by any of those
known keywords are automatically skipped. If many PO files are opened
simultaneously, each one has its own independent set of known keywords.
There is no provision in PO mode, currently, for deleting a known
keyword, you have to quit the file (maybe using <KBD>q</KBD>) and reopen
it afresh. When a PO file is newly brought up in an Emacs window, only
<SAMP>`gettext´</SAMP> and <SAMP>`_´</SAMP> are known as keywords, and <SAMP>`gettext´</SAMP>
is preferred for the <KBD>M-.</KBD> command. In fact, this is not useful to
prefer <SAMP>`_´</SAMP>, as this one is already built in the <KBD>M-,</KBD> command.
</P>
<H2><A NAME="SEC18" HREF="gettext_toc.html#TOC18">3.5 Special Comments preceding Keywords</A></H2>
<P>
<A NAME="IDX144"></A>
In C programs strings are often used within calls of functions from the
<CODE>printf</CODE> family. The special thing about these format strings is
that they can contain format specifiers introduced with <KBD>%</KBD>. Assume
we have the code
</P>
<PRE>
printf (gettext ("String `%s' has %d characters\n"), s, strlen (s));
</PRE>
<P>
A possible German translation for the above string might be:
</P>
<PRE>
"%d Zeichen lang ist die Zeichenkette `%s'"
</PRE>
<P>
A C programmer, even if he cannot speak German, will recognize that
there is something wrong here. The order of the two format specifiers
is changed but of course the arguments in the <CODE>printf</CODE> don't have.
This will most probably lead to problems because now the length of the
string is regarded as the address.
</P>
<P>
To prevent errors at runtime caused by translations the <CODE>msgfmt</CODE>
tool can check statically whether the arguments in the original and the
translation string match in type and number. If this is not the case
and the <SAMP>`-c´</SAMP> option has been passed to <CODE>msgfmt</CODE>, <CODE>msgfmt</CODE>
will give an error and refuse to produce a MO file. Thus consequent
use of <SAMP>`msgfmt -c´</SAMP> will catch the error, so that it cannot cause
cause problems at runtime.
</P>
<P>
If the word order in the above German translation would be correct one
would have to write
</P>
<PRE>
"%2$d Zeichen lang ist die Zeichenkette `%1$s'"
</PRE>
<P>
The routines in <CODE>msgfmt</CODE> know about this special notation.
</P>
<P>
Because not all strings in a program must be format strings it is not
useful for <CODE>msgfmt</CODE> to test all the strings in the <TT>`.po´</TT> file.
This might cause problems because the string might contain what looks
like a format specifier, but the string is not used in <CODE>printf</CODE>.
</P>
<P>
Therefore the <CODE>xgettext</CODE> adds a special tag to those messages it
thinks might be a format string. There is no absolute rule for this,
only a heuristic. In the <TT>`.po´</TT> file the entry is marked using the
<CODE>c-format</CODE> flag in the <KBD>#,</KBD> comment line (see section <A HREF="gettext_2.html#SEC9">2.2 The Format of PO Files</A>).
</P>
<P>
<A NAME="IDX145"></A>
<A NAME="IDX146"></A>
The careful reader now might say that this again can cause problems.
The heuristic might guess it wrong. This is true and therefore
<CODE>xgettext</CODE> knows about special kind of comment which lets
the programmer take over the decision. If in the same line or
the immediately preceding line of the <CODE>gettext</CODE> keyword
the <CODE>xgettext</CODE> program find a comment containing the words
<KBD>xgettext:c-format</KBD> it will mark the string in any case with
the <KBD>c-format</KBD> flag. This kind of comment should be used when
<CODE>xgettext</CODE> does not recognize the string as a format string but
is really is one and it should be tested. Please note that when the
comment is in the same line of the <CODE>gettext</CODE> keyword, it must be
before the string to be translated.
</P>
<P>
This situation happens quite often. The <CODE>printf</CODE> function is often
called with strings which do not contain a format specifier. Of course
one would normally use <CODE>fputs</CODE> but it does happen. In this case
<CODE>xgettext</CODE> does not recognize this as a format string but what
happens if the translation introduces a valid format specifier? The
<CODE>printf</CODE> function will try to access one of the parameter but none
exists because the original code does not refer to any parameter.
</P>
<P>
<CODE>xgettext</CODE> of course could make a wrong decision the other way
round, i.e. a string marked as a format string actually is not a format
string. In this case the <CODE>msgfmt</CODE> might give too many warnings and
would prevent translating the <TT>`.po´</TT> file. The method to prevent
this wrong decision is similar to the one used above, only the comment
to use must contain the string <KBD>xgettext:no-c-format</KBD>.
</P>
<P>
If a string is marked with <KBD>c-format</KBD> and this is not correct the
user can find out who is responsible for the decision. See
section <A HREF="gettext_4.html#SEC21">4.1 Invoking the <CODE>xgettext</CODE> Program</A> to see how the <KBD>--debug</KBD> option can be
used for solving this problem.
</P>
<H2><A NAME="SEC19" HREF="gettext_toc.html#TOC19">3.6 Special Cases of Translatable Strings</A></H2>
<P>
<A NAME="IDX147"></A>
The attentive reader might now point out that it is not always possible
to mark translatable string with <CODE>gettext</CODE> or something like this.
Consider the following case:
</P>
<PRE>
{
static const char *messages[] = {
"some very meaningful message",
"and another one"
};
const char *string;
...
string
= index > 1 ? "a default message" : messages[index];
fputs (string);
...
}
</PRE>
<P>
While it is no problem to mark the string <CODE>"a default message"</CODE> it
is not possible to mark the string initializers for <CODE>messages</CODE>.
What is to be done? We have to fulfill two tasks. First we have to mark the
strings so that the <CODE>xgettext</CODE> program (see section <A HREF="gettext_4.html#SEC21">4.1 Invoking the <CODE>xgettext</CODE> Program</A>)
can find them, and second we have to translate the string at runtime
before printing them.
</P>
<P>
The first task can be fulfilled by creating a new keyword, which names a
no-op. For the second we have to mark all access points to a string
from the array. So one solution can look like this:
</P>
<PRE>
#define gettext_noop(String) String
{
static const char *messages[] = {
gettext_noop ("some very meaningful message"),
gettext_noop ("and another one")
};
const char *string;
...
string
= index > 1 ? gettext ("a default message") : gettext (messages[index]);
fputs (string);
...
}
</PRE>
<P>
Please convince yourself that the string which is written by
<CODE>fputs</CODE> is translated in any case. How to get <CODE>xgettext</CODE> know
the additional keyword <CODE>gettext_noop</CODE> is explained in section <A HREF="gettext_4.html#SEC21">4.1 Invoking the <CODE>xgettext</CODE> Program</A>.
</P>
<P>
The above is of course not the only solution. You could also come along
with the following one:
</P>
<PRE>
#define gettext_noop(String) String
{
static const char *messages[] = {
gettext_noop ("some very meaningful message",
gettext_noop ("and another one")
};
const char *string;
...
string
= index > 1 ? gettext_noop ("a default message") : messages[index];
fputs (gettext (string));
...
}
</PRE>
<P>
But this has a drawback. The programmer has to take care that
he uses <CODE>gettext_noop</CODE> for the string <CODE>"a default message"</CODE>.
A use of <CODE>gettext</CODE> could have in rare cases unpredictable results.
</P>
<P>
One advantage is that you need not make control flow analysis to make
sure the output is really translated in any case. But this analysis is
generally not very difficult. If it should be in any situation you can
use this second method in this situation.
</P>
<P><HR><P>
Go to the <A HREF="gettext_1.html">first</A>, <A HREF="gettext_2.html">previous</A>, <A HREF="gettext_4.html">next</A>, <A HREF="gettext_22.html">last</A> section, <A HREF="gettext_toc.html">table of contents</A>.
</BODY>
</HTML>
|
