C: Underscore before string?

tinyTux · 03-23-2011, 11:33 AM

I have been reading through C source code to try to improve myself. In the coreutils source code, there are often function calls like so:

Code:

fprintf (stderr, _("Try `%s --help' for more information.\n"), program_name);

Why is that string in the middle surrounded by parentheses and preceded by an underscore?

corp769 · 03-23-2011, 11:36 AM

The underscore is just an identifier. Either the program itself or a library uses it, and defines it as a function or a macro. _() Might return the text inside of fprint to translate to a different language, add formatting, etc. Hope that helps.

Josh

wje_lq · 03-23-2011, 02:06 PM

Sprinkled throughout the coreutils code are macro definitions of the form

Code:

#define _(fred) gettext (fred)

There are 28 of those, at last count.

They don't use fred, of course, and it doesn't matter what they use; the macro _ is defined as a call to gettext() with the argument to the macro. gettext() returns a string. For more details on gettext(), see the man page.

Nominal Animal · 03-23-2011, 02:09 PM

If you read the sources carefully, you will very likely find something like

Code:

#ifdef  HAVE_GETTEXT
#define _(s) gettext(s)
#else
#define _(s) s
#endif

Like corp769 said, _() is usually a macro used to make string localization easier. The above way also allows the same code to be compiled without localization support without changing any code. For details, see eg. man 3 gettext.

bigearsbilly · 03-24-2011, 04:15 AM

don't be too alarmed,
if you read through the source code of standard libraries or
kernel code, you often find that your brain explodes.

this is normal
:-)

wje_lq · 03-24-2011, 05:17 AM

Quote:

Originally Posted by bigearsbilly

if you read through the source code of standard libraries or
kernel code, you often find that your brain explodes.

It's not brain science.

tinyTux · 03-24-2011, 11:21 AM

Thanks. I'll admit, I haven't read all the source code yet but am working on it. I must have missed that macro definition. I assumed it was some kind of special C construct I hadn't heard about yet.