格式字符串周围的“ TEXT”在“ printf”中是什么意思

Question

The following prints the percentage of memory used.

  printf (TEXT("There is  %*ld percent of memory in use.\n"),
            WIDTH, statex.dwMemoryLoad);

WIDTH is defined to be equal to 7.

What does TEXT mean, and where is this sort of syntax defined in printf?

Answer 1

As others already said, TEXT is probably a macro.

To see what they become, simply look at the preprocessor output. If are using gcc:

gcc -E file.c

Answer 2

TEXT() is probably a macro or function which returns a string value. I think it is user defined and does some manner of formatting on that string which is passed as an argument to the TEXT function. You should go to the function declaration for TEXT() to see what exactly it does.

Answer 3

Just guessing but TEXT is a char* to char* function that takes care of translating a text string for internationalization support.

Note that if this is the case then may be you are also required to always use TEXT with a string literal (and not with expressions or variables) to allow an external tool to detect all literals that need translations by a simple scan of the source code. For example may be you should never write:

puts(TEXT(flag ? "Yes" : "No"));

and you should write instead

puts(flag ? TEXT("Yes") : TEXT("No"));

Something that is instead standard but not used very often is the parameteric width of a field: for example in printf("%*i", x, y) the first parameter x is the width used to print the second parameter y as a decimal value.

When used with scanf instead the * special char can be used to specify that you don't want to store the field (ie to "skip" it instead of reading it).

Answer 4

_TEXT() or _T() is a microsoft specific macro. This MSDN link says

To simplify code development for various international markets,  
the Microsoft run-time library provides Microsoft-specific "generic-text" mappings for many data types,  routines, and other objects.  
These mappings are defined in TCHAR.H.  
You can use these name mappings to write generic code that can be compiled for any of the three kinds of character sets:  
ASCII (SBCS), MBCS, or Unicode, depending on a manifest constant you define using a #define statement.  
Generic-text mappings are Microsoft extensions that are not ANSI compatible.  

_TEXT is a macro to make a strings "character set neutral". For example _T("HELLO");

Characters can either be denoted by 8 bit ANSI standards or the 16 bit Unicode notation.

If you define _TEXT for all strings and define a preprocessor symbol "_UNICODE", all such strings will follow UNICODE encoding. If you don't define _UNICODE, the strings will all be ANSI. Hence the macro _TEXT allows you to have all strings as UNICODE or ANSI. So no need to change every time you change your character set.

Answer 5

TEXT() is a unicode support macro defined in winnt.h . If UNICODE is defined then it prepends L to the string making it wide.

Also see TEXT vs. _TEXT vs. _T, and UNICODE vs. _UNICODE blog post.