C

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.

Embedded C

Some tips to make embedded development with C.

Enums are not always int

Some compilers do not necessarily map enum types to int. The ARM compiler for instance will by default use the smallest date type that can hold the value of all enumerators.

typedef enum MyEnum_t {
  first     = 1,
  second    = 2,
  _forceint = 0x7FFFFFFF             // To force 32-bit (signed) enum
} MyEnum_t;

Win32 vs Linux

Linux	Win32	Comment
snprintf	_snprintf	deprecated, replaced by _snprintf_s but not compatible