Using printf Effectively in Java Make PDF-417 2d barcode in Java Using printf Effectively

Using printf Effectively using jsp todraw pdf 417 with web,windows application CBC Based on the pr PDF-417 2d barcode for Java evious discussion, perhaps one of the most important things to know about using printf is knowing when not to use it. If you can t avoid it, you can at least turn it off when you don t need it. 10.

2.2.1 Preprocessor Help The C preprocessor can be very helpful for formatting and controlling debug messages.

One useful pattern is to wrap calls to printf in a macro, which can be used to cut down on clutter and also allows you remove the messages easily when they re not needed. For example:. #ifdef DEBUG #d efine DEBUGMSG(...

) printf(__VA_ARGS__) #else #define DEBUGMSG /* nop */ #endif /* Uses a C99 / GNU extension */. 1. Devices such Java PDF417 as hard drives have internal cache as well, which may not be flushed when this function returns. There is no standard way to control the drive s internal cache.

. 10 Debugging Using variable jar pdf417 2d barcode argument lists in macros began as a GNU extension but was adopted by the C99 standard as well. If you are using a non-GNU compiler or one that does not support C99 extensions, there is a more clumsy alternative syntax that gives you the effect of variable argument lists:. #define DEBUGMS G(msg) printf msg /* Only works like this ...

*/ DEBUGMSG(("Hello World %d\n",123)); */ /* Caller passes in the parentheses. */. /* becomes prin tomcat pdf417 2d barcode tf("Hello World %d\n",123);. Note the double parentheses enclosing the arguments. The inner parentheses become part of the macro argument, which is why they are left off in the definition. This is a bit awkward, a bit ugly, and hard to explain, but it is a useful substitute for variable argument lists in macros.

Wrapping printf calls in a macro also allows you to hide much ugliness that can otherwise be useful. You can include a filename and line number in each message as follows:. #define DEBUGMS applet PDF 417 G(fmt,...

) printf("%s %d " fmt, __FILE__,__LINE__, ## __VA_ARGS__). The double poun d sign, used in this context, is another GNU-only extension. Normally, this is used for string concatenation inside a macro, but in this context, GNU assigns a different meaning. When used with __VA_ARGS__ it strips the trailing comma for you when you use the macro with a format string that takes no arguments.

That is, if __VA_ARGS__ is empty, gcc will remove the trailing comma for you. Without this extension, you would be required to provide at least one argument even when the format strings take no arguments. Note that the format string "%s %d" is concatenated with the fmt argument by the C compiler not the C preprocessor.

Concatenating fixed strings like this has been a feature of C since the original ANSI (1989) standard.. Quick and Dirty Preprocessor Tricks Here are some of my favorite printf tricks using the C preprocessor. The Most Basic Debugging Tool: printf Printing Variables to the Screen with Minimal Typing #define PHEX(x) servlet PDF417 printf("%#10x %s\n", x, #x) ...

PHEX(foo); PHEX(bar); PHEX(averylongname);. The trick here is using the # character to wrap a macro argument in quotes. The preprocessor expands arguments that are preceded with a # by enclosing this in quotes. This can save some typing.

The following line. PHEX(averylongname);. expands to printf("%#10x % applet PDF417 s\n", averylongname, "averylongname");. The other trick is to put the values in a fixed-width field on the left. I find that the output is much easier to read, because the variable names can vary all over the map but the values always line up. For example:.

0x1 foo 0x2 bar 0xdeadbeef averylongname I used hexadeci mal in this example, but you can use this trick for whatever format you like. The magic is on the right side of the format string..

Inline Synchronization Based on the ea rlier discussion of synchronization, it s possible to wrap this ugliness in a macro to cut down on clutter. One solution could look like this:. #define DEBUGMS PDF417 for Java G(...

) \ do { \ printf(__VA_ARGS__);\ fflush(stdout);\ } while(0). You can stuff a nything you need to in this block of code. If this block of code grows over time, it may start to affect the size of your code. It may be time to create a function instead.

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