Switch Statement in C

Question

I have the following if-statements:

    if (strcmp(registerName, "zero"))
            return 00000;
    else if (strcmp(registerName, "at"))
        return 00001;
    else if (strcmp(registerName, "v0"))
        return 00010;
    else if (strcmp(registerName, "v1"))
        return 00011;

It's actually really long - about 20 if-statements. Therefore, I would like to use a switch. How would I convert that to switch when each statement has a different condition?

I tried something as the code below, but it does not work:

int registerAddress;

switch(registerAddress) {

case 1 (strcmp(registerName, "zero")):
        regsiterAddress = 00000;
        break;
case 2 (strcmp(registerName, "at")):
        registerAddress = 00001;
        break;
}

Answer 1

You can't — switch statements in C only work on primitive types, not on strings. You could use, say, a hash table or a search tree to optimize the matching, but for only 20 options that may not be worth the trouble.

What you could do, to clean up the code, is set up a mapping table:

struct str2Num {
    char *str;
    int num;
};

const struct str2Num registerMap[] = {
    { "zero", 00000 },
    { "at", 00001 },
    { "v0", 00010 },
    { "v1", 00011 },
    { NULL, 0 }  /* end marker */
};

and do your matching like this:

int i;
for (i = 0; registerMap[i].str != NULL; i++) {
    if (strcmp(registerName, registerMap[i].str) == 0) {
        return registerMap[i].num;
    }
}
/* handle no-match case here */

In fact, if you sorted the table alphabetically, you could even use bsearch() for fast matching.

Answer 2

You can only switch on integers, so this will not work.

If all you're doing is converting a string to an int, store the info in an array and look through it.

struct {
   const char *name;
   int value;
} fooMapping[] = {
     {"zero",0},
     {"at",1}
      ....
};

int foo2value(const char *name)
{
     size_t i;
     for(i = 0; i < sizeof fooMapping/sizeof fooMapping[0]; i++) {
          if(strcmp(name, fooMapping[i].name) == 0) 
             return fooMapping[i].value;

     }
    return -1;
}