{"id":14211,"date":"2026-06-03T02:00:00","date_gmt":"2026-06-03T06:00:00","guid":{"rendered":"https:\/\/www.both.org\/?p=14211"},"modified":"2026-05-19T12:38:46","modified_gmt":"2026-05-19T16:38:46","slug":"spaces-in-dos-filenames-part-2","status":"publish","type":"post","link":"http:\/\/www.both.org\/?p=14211","title":{"rendered":"Spaces in DOS filenames, part 2"},"content":{"rendered":"
\r\n
\r\n \r\n <\/i>\r\n <\/a>\r\n <\/span>\r\n<\/div><\/div>\n

I recently answered a question about “can FreeDOS use spaces in filenames?” The short answer is yes, if the spaces are between other characters<\/a> in the filename. I gave an example that you can have a file named MY\u23b5FILE.TXT<\/code> with the space in the middle, but not MYFILE\u23b5.TXT<\/code> where the space is after the base name<\/em> in the filename. (In this example, I’ve typed each space as \u23b5<\/code> so you can see it.) Let’s explore why DOS filenames have this limitation with spaces.<\/p>\n\n\n\n

8.3 filenames<\/h2>\n\n\n\n

DOS saves files using a File Allocation Table<\/a> where filenames are stored in a particular way<\/a>: the first two fields are the filename<\/em> and extension<\/em>. The filename<\/em> is always stored as 8 characters, and the extension is always 3 characters.<\/p>\n\n\n\n

Each field is padded with spaces. That means if you save a file as FILE.C<\/code>, that’s 4 characters for the filename<\/em> part and 1 character for the extension<\/em>. Behind the scenes, DOS saves this as an “8.3” filename, with extra character padded as spaces: FILE\u23b5\u23b5\u23b5\u23b5.C\u23b5\u23b5<\/code>.<\/p>\n\n\n\n

A test program<\/h2>\n\n\n\n

Let’s create a short test program that saves a new file using a space at the end<\/em> of the filename<\/em> part. In this case, we’ll write a text file called BB\u23b5.TXT<\/code> (there’s a space after the BB<\/code> and before the .TXT<\/code>) that saves just as single line of text.<\/p>\n\n\n\n

<\/a>#include <stdio.h>\n<\/a>\n<\/a>int main()\n<\/a>{\n<\/a>  FILE *f;\n<\/a>\n<\/a>  f = fopen(\"BB .TMP\", \"w\");\n<\/a>  if (f==NULL) {\n<\/a>    puts(\"error, cannot open file\");\n<\/a>    return 1;\n<\/a>  }\n<\/a>\n<\/a>  fputs(\"Hello world\\n\", f);\n<\/a>  fclose(f);\n<\/a>\n<\/a>  puts(\"Ok\");\n<\/a>  return 0;\n<\/a>}<\/code><\/pre>\n\n\n\n
Just to explain a few things here: the fopen<\/code> statement opens a file called BB\u23b5.TMP<\/code> for w<\/strong>riting. If this file doesn’t exist, the program will create it automatically. Then it saves the text Hello world<\/code> to the file, and closes it before the program ends.<\/p>\n\n\n\n
You can compile this program using any C compiler. On FreeDOS, we include several C compiler in the FreeDOS distribution, including Open Watcom C, IA-16 GCC, and BCC; these are all in the “Development” package group on the BonusCD. Let’s save this test program as bb.c<\/code> and compile it using Open Watcom C:<\/p>\n\n\n\n
D:\\SRC>wcl -q bb.c\nDOS\/4GW Protected Mode Run-time  Version 1.97\nCopyright (c) Rational Systems, Inc. 1990-1994\nDOS\/4GW Protected Mode Run-time  Version 1.97\nCopyright (c) Rational Systems, Inc. 1990-1994<\/code><\/pre>\n\n\n\n
The -q<\/code> command line option makes Open Watcom run in q<\/strong>uiet mode, so it doesn’t print any extra text. The other output you see isn’t actually from the C compiler, but from the DOS\/4GW program, which is a DOS “extender” that Open Watcom uses. If you don’t want this extra output, set the DOS4G<\/code> environment variable to quiet<\/code> and DOS\/4GW won’t print anything. Let’s compile with Open Watcom C one more time, with DOS\/4GW running in “quiet” mode, but without Open Watcom’s -q<\/code> command line option, to show the normal compiler output:<\/p>\n\n\n\n
D:\\SRC>set DOS4G=quiet\nD:\\SRC>wcl bb.c\nOpen Watcom C\/C++16 Compile and Link Utility Version 1.9\nPortions Copyright (c) 1988-2002 Sybase, Inc. All Rights Reserved.\nSource code is available under the Sybase Open Watcom Public License.\nSee http:\/\/www.openwatcom.org\/ for details.\n        wcc BB.C\nOpen Watcom C16 Optimizing Compiler Version 1.9\nPortions Copyright (c) 1984-2002 Sybase, Inc. All Rights Reserved.\nSource code is available under the Sybase Open Watcom Public License.\nSee http:\/\/www.openwatcom.org\/ for details.\nBB.C: 18 lines, included 771, 0 warnings, 0 errors\nCode size: 59\n        wlink @__wcl__.lnk\nOpen Watcom Linker Version 1.9\nPortions Copyright (c) 1985-2002 Sybase, Inc. All Rights Reserved.\nSource code is available under the Sybase Open Watcom Public License.\nSee http:\/\/www.openwatcom.org\/ for details.\nloading object files\nsearching libraries\ncreating a DOS executable<\/code><\/pre>\n\n\n\n
That’s a lot of extra text. You can see why I usually compile using the -q<\/code> (q<\/strong>uiet) command line option.<\/p>\n\n\n\n
Spaces in filenames<\/h2>\n\n\n\n
After compiling the test program, let’s run it to create a new BB\u23b5.TMP<\/code> file:<\/p>\n\n\n\n
D:\\SRC>bb.exe\nOk<\/code><\/pre>\n\n\n\n
The program prints an Ok<\/code> message to indicate it was able to save a new file called BB\u23b5.TMP<\/code>. But if we look for the new file, we’ll see that it doesn’t have the space after the BB<\/code> filename<\/em> part:<\/p>\n\n\n\n
D:\\SRC>dir \/b *.tmp\nBB.TMP<\/code><\/pre>\n\n\n\n
This is because the DOS filesystem pads out the 8-character filename with spaces, so BB\u23b5.TMP<\/code> actually gets saved as BB\u23b5\u23b5\u23b5\u23b5\u23b5\u23b5.TMP<\/code> (that’s BB<\/code> plus 6 spaces, then the TMP<\/code> extension). In fact, saving a file like BB.TMP<\/code> would also get stored the same way: BB<\/code> plus 6 spaces, then the extension.<\/p>\n","protected":false},"excerpt":{"rendered":"
DOS filenames are 8.3, space padded, so you cannot have spaces at the end<\/p>\n","protected":false},"author":33,"featured_media":3514,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","footnotes":""},"categories":[340,150],"tags":[267,152],"class_list":["post-14211","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-freedos","category-programming","tag-freedos","tag-programming"],"modified_by":"Jim Hall","_links":{"self":[{"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/14211","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/users\/33"}],"replies":[{"embeddable":true,"href":"http:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=14211"}],"version-history":[{"count":1,"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/14211\/revisions"}],"predecessor-version":[{"id":14212,"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/14211\/revisions\/14212"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/media\/3514"}],"wp:attachment":[{"href":"http:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=14211"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=14211"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=14211"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}