The sos home page

Instructions for downloading and using sos are here.

Please note that sos have three modes:

• "-p", the default option, generates C Pre-Processor definitions. Case labels are made of [a-z,_,0-9,A-Z].

• "-s", generates a switch statement skeleton. Case labels are made of [a-z,_,0-9,A-Z].

• "-f", accepts arbitrary byte case labels. Generates switch statement skeleton.

The switch skeleton mode is preferable for two reasons:

• collisions with predefined macros, C keywords etc are eliminated. The CPP code will detect such collisions and stop the compilation, if placed after all other CPP code (#include, #define, etc) but why get into such trouble for a slightely nicer code?
• case labels which are not legal names can be used (with the "-f" option).

Note that the development version of sos (nsos) can process suitable input to create switch statements nested inside another switch. This is very useful to scan a file composed of attribute/value pairs. For example, this input will generate the following output.

This example can be downloaded here. The distribution copy can be compiled using "make examples".

The following "#define" directives and sos10q prototype were generated by the "-p" option and were simplified somewhat to enhance clarity (the collision detection CPP code was removed).

 

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* code generated by sos */
long long int sos10q(char *) ;
#define  sos_switch(x)  switch(sos10q(x)) 
#define  red                                          74052ULL 
#define  blue                                        574789ULL 
#define  black                                     36704459ULL 
#define  violet                                 23777296724ULL 
#define  aquamarine                       22891914789950341ULL  /* check! */
/* end of generated code */

int main()
  {
  int   n ;
  char  sp[100] ;

  while(1)
    {
    puts("Enter a color in lowercase (CTRL-D to exit): ") ;
    n = scanf("%99s", sp) ;
    if (n != 1) exit(EXIT_FAILURE) ;

    sos_switch(sp)
      {
      case (red) : 
        printf("I see red \n") ;
        break ;
      case (blue) : 
        printf("I see blue \n") ;
        break ;
      case (black) : 
        printf("I see black \n") ;
        break ;
      case (violet) : 
        printf("I see violet \n") ;
        break ;
      case (aquamarine) :                   /* > 9 chars */
        if (strcmp("aquamarine", sp)) goto nocolor ;
        printf("I see aquamarine \n") ;
        break ;
      default:
      nocolor:
        printf("Sorry, unrecognized colour...\n") ;
      }
    }
  }

Note the strcmp invalid input check for "AQUAMARINE".

The round parentheses around the case values are not required but they serve as a visual aid and may help the compiler to spot problems.

This example can be downloaded here. The distribution copy can be compiled with "make examples".

The following skeleton code was generated by sos "-s" option and somewhat simplified to enhance clarity:

long long int sos10q(char *) ;
#define sos_switch(x) switch(sos10q(x))

sos_switch(your-string-ptr) 
  { 
  case                74052ULL :            /* "red" */ 
    ... 
    break ; 
  case               574789ULL :            /* "blue" */ 
    ... 
    break ; 
  case             36704459ULL :            /* "black" */ 
    ... 
    break ; 
  case          23777296724ULL :            /* "violet" */ 
    ... 
    break ; 
  case    22891914789950341ULL :            /* "aquamarine" */ 
    if (strcmp("aquamarine", your-string-ptr)) goto badsink ; 
    ... 
    break ; 
  default : 
  badsink : 
    fprintf(stderr, "sos: unrecognized input... \n") ; 
    ... 
  } 
 

Note the generated code provides the original string in a comment and even the "strcmp" check. Beware, if you have more than one generated switch in a function the check labels must be different.