C
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References
- The C Library Reference Guide
- C Preprocessor reference
- manpage manpages-dev
- manpage manpages-posix-dev
sudo apt-get install manpages-dev manpages-posix-dev
Tips
Struct Initializer
struct {
int a;
int b;
} s = { .a = 1, .b = 2 };
Same applies for union.
Variadic Macros
See reference here.
#define eprintf(...) fprintf (stderr, __VA_ARGS__)
/* eprintf ("%s:%d: ", input_file, lineno)
==> fprintf (stderr, "%s:%d: ", input_file, lineno) */
#define eprintf(args...) fprintf (stderr, args)
#define eprintf(format, ...) fprintf (stderr, format, __VA_ARGS__)
An handy macro hack that counts the number of parameters passed before expansion (See [1] and [2]):
/* The PP_NARG macro returns the number of arguments that have been
* passed to it. This compensates for lack of __VA_NARGS__.
* Macros written by Laurent Deniau See http://en.wikipedia.org/wiki/Variadic_macro.
*/
#define PP_NARG(...) \
PP_NARG_(__VA_ARGS__,PP_RSEQ_N())
#define PP_NARG_(...) \
PP_ARG_N(__VA_ARGS__)
#define PP_ARG_N( \
_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,N,...) N
#define PP_RSEQ_N() \
63,62,61,60, \
59,58,57,56,55,54,53,52,51,50, \
49,48,47,46,45,44,43,42,41,40, \
39,38,37,36,35,34,33,32,31,30, \
29,28,27,26,25,24,23,22,21,20, \
19,18,17,16,15,14,13,12,11,10, \
9,8,7,6,5,4,3,2,1,0
/* Some test cases */
PP_NARG(A) -> 1
PP_NARG(A,B) -> 2
PP_NARG(A,B,C) -> 3
PP_NARG(A,B,C,D) -> 4
PP_NARG(A,B,C,D,E) -> 5
PP_NARG(1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
1,2,3) -> 63
Variadic I/O Functions
See [3] for some reference information on variable functions.
The standard variadic I/O functions are:
#include <stdio.h>
#include <stdarg.h>
int vprintf(const char *format, va_list ap);
int vfprintf(FILE *stream, const char *format, va_list ap);
int vsprintf(char *str, const char *format, va_list ap);
int vsnprintf(char *str, size_t size, const char *format, va_list ap);
Example of use:
//This works both on win32 / linux
#include <stdio.h>
#include <stdarg.h>
void vario(const char* formatstr,...)
{
va_list args;
va_start(args, formatstr);
vprintf(formatstr, args);
va_end(args); /* cleanup - DON'T FORGET */
}
Note on win32:
- There exists alternative functions ([4]) prefixed with a '_', such as
_vprintf_p
,_vfprintf_l
, ...
Temporary variable names for Macro
/* UNIQ(x) creates a unique variable name that depends on the current source line as returned by __LINE__. We need
Several intermediate macros because identifier are not expanded in macro if they are used along with # or ## in
macro definition.
Example: #define SCAN_MY(var,n) {int UNIQ(x); for(UNIQ(x)=0; UNIQ(x)<n; ++UNIQ(x)) printf(var[UNIQ(x)]);}
*/
#define UNIQ__(x,y) x ## y
#define UNIQ_(x,y) UNIQ__(x,y)
#define UNIQ(x) UNIQ_(x,__LINE__)
Debugging
See general page on Debugging.
Win32 vs Linux
Linux | Win32 | Comment |
---|---|---|
snprintf |
_snprintf |
deprecated, replaced by _snprintf_s but not compatible
|