rd235 / strcase

Multiway branch (switch) for short strings in C (in one header file)

strcase

Multiway branch (switch) for short strings in C (in one header file)

#include <stdio.h>
#include <strcase.h>

int main(int argc, char * argv[]) {
  printf("%llx %llx \n", strcase("ciao"), STRCASE(c,i,a,o));
  printf("%llx %llx \n", strcase("verylong"), STRCASE(v,e,r,y,l,o,n,g));
  printf("%llx %llx \n", strcase("far_toolong"), STRCASE(f,a,r,_,t,o,o,l,o,n,g));
  printf("%llx %llx \n", strcase("far_tool"), STRCASE(f,a,r,_,t,o,o,l));
  for (argv++; *argv; argv++) {
    switch(strcase(*argv)) {
      case STRCASE(o,n,e): printf("1\n"); break;
      case STRCASE(t,w,o): printf("2\n"); break;
      case STRCASE(t,h,r,e,e): printf("3\n"); break;
      case STRCASE(f,o,r,t,y,f,o,u,r): printf("44\n"); break;
      case STRCASE(f,o,r,t,y,t,w,o): printf("42\n"); break;
    }
  }
}

strcase provides one inline function strcase, strcase_tolower and a macro STRCASE, both convert a string in a uint64_t integer value. Only the first 8 characters are significative.

strcase_tolower works like strcase but it converts uppercase letters as if they were lowercase.

strcase or strcase_tolower can be used in the expression of a switch statement to convert a string to an integer type, STRCASE generates at compile time the integer constants that can be used for the case stanzas of the switch.

Actually STRCASE:

• requires the string to be specified as comma separated characters e.g. STRCASE(h,e,l,p)
• supports "strings" using only literals, digits and underscore. Other symbols can appear using their name, as in: STRCASE(slash,e,t,c)

When the string contains only one char, the value of strcase is the code of the character (e.g. the value of strcase("a") as well as the value of STRCASE(a) is 'a')

Regardless of its limitations this macro library is quite useful to write switch statements in C language using strings (almost) as if it were integers (as in the example above). Although STRCASE needs commas between characters the string is still readable, and it is simple to add cases or change the tags. This is a simple example:

int yes_or_not(const char *s) {
  switch (strcase_tolower(s)) {
    case STRCASE(y,e,s):
    case 'y':
        return 1;
    case STRCASE(n,o):
    case 'n':
        return 0:
    default:
        return -1;
  }
}

Given that I am going to use this in several projects of mine, I decided to publish it as a tiny independent project.

renzo, June 4 2018

Strcase is a portable alternative to multi-character constants in C.

When the string contains only one char, the value of strcase is the code of the character (e.g. the value of strcase("a") as well as the value of STRCASE(a) is 'a').

update for C++ users

Now strcase is available for C++ users, too. Due to the higher level of flexibility of constant management in C++ the STRCASE macro can use standard strings. THe same example above in C++ becomes:

int yes_or_not(const char *s) {
  switch (strcase_tolower(s)) {
    case STRCASE("yes"):
    case 'y':
        return 1;
    case STRCASE("no"):
    case 'n':
        return 0:
    default:
        return -1;
  }
}

(credit: thanks to mcpiroman who proposed this extension for C++ users)

how to install strcase

Just put strcase.h where you need it and that's all, folks.

In case you are lazy and you like standard install methods and tools, I have added a trivial CMake support. The standard cmake install sequence applies:

$ cmake .
$ sudo make install