How Can I Implement Switch Statements with Non-Integer Values in C/C ?

C/C : Switch Statements for Non-Integral Values

In switch statements, it is often necessary to perform actions based on non-integer values. Unfortunately, in C/C , switch statements can only be used with integer expressions.

The Straightforward Approach

A simple solution for handling non-integral switch statements is to use a series of if-else statements:

if (str == "foo") {
  ...
} else if (str == "bar") {
  ...
} else {
  ...
}

However, this approach is verbose, inefficient (O(n), where n is the number of cases), and lacks the elegance of a switch statement.

Macro and Template Tricks

Using macros and templates, it is possible to implement binary search at compile time:

#define NEWMATCH
MATCH("asd")
  some c++ code
MATCH("bqr")
  ... the buffer for the match is in _buf
MATCH("zzz")
  ...  user.YOURSTUFF 
/*ELSE 
  optional
*/
ENDMATCH(xy_match)

This generates a function xy_match that automatically performs binary search and invokes the appropriate code for each case. This approach is efficient (O(log n)), but it is not as straightforward as a standard switch statement.

C 11 Enhancements

C 11 introduced lambdas and initializer lists, which greatly improve the clarity of non-integer switch statements:

template <typename KeyType, typename FunPtrType, typename Comp>
void Switch(const KeyType &amp;value,std::initializer_list<std::pair<const KeyType,FunPtrType>> sws,Comp comp) {
  auto r=std::lower_bound(sws.begin(),sws.end(),val,cmp);
  if ( (r!=sws.end())&amp;&amp;(!cmp(val,*r)) ) {
    r->second();
  }
}

This template provides a concise and efficient way to implement non-integer switch statements.

Compile Time Trie

A more recent advancement involves utilizing metaprogramming to generate a search trie at compile time. This approach handles unsorted non-integral switch statements and generates efficient code using the compiler's code generator:

Switch<const char *,void (*)()>("ger",{ // sorted: 
  {"asdf",[]{ printf("0\n"); }},
  {"bde",[]{ printf("1\n"); }},
  {"ger",[]{ printf("2\n"); }}
},[](const char *a,const char *b){ return strcmp(a,b)<0;}); 

This approach further enhances the efficiency and readability of non-integer switch statements in C/C .

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