Translation array

Question

I need to make a simple translator. For example:

• input: "foo" output: "bar"
• input: "the" output: "teh"
• input: "what" output: "wut"

I know I can write it like this:

if (!strcmp(input, "foo"))
    puts("bar");
else if (!strcmp(input, "the"))
    puts("teh");
else if (!strcmp(input, "what"))
    puts("wut");

But that's big and messy. Is there a shortcut to do this? I know that in PHP (sorry for the inevitable syntax errors, I'm not proficient) there's something like this:

value = array(
    "foo" => "bar",
    "the" => "teh",
    "what" => "wut"
);

How can I shorten the original code using something like a PHP array?

Answer 1

You can define a struct, which contains the word and the translation:

typedef struct {
    const char *word;
    const char *translation;
} translate_t;

Then you can just create an array of structs like this:

const translate_t translate[] = {{"foo", "bar"},
                                 {"the", "teh"},
                                 {"what", "wut"}};

If you want print out the words and translations, then you can just do this:

size_t size = sizeof translate/sizeof *translate;

for (size_t i = 0; i < size; i++) {
    printf("Word: %s Translation: %s\n", translate[i].word, translate[i].translation);
}

Which will output:

Word: foo Translation: bar
Word: the Translation: teh
Word: what Translation: wut

This is a good approach for associating a word with a translation.

UPDATE: @Olaf suggested using a macro for size, which is far better for declaring sizes of arrays. Therefore, the above code can be expressed as:

#define ARRAY_SIZE(x) ((sizeof x)/sizeof *x) /* near top, or before main() is a good place for this */

for (size_t i = 0; ARRAY_SIZE(translate); i++) {
    printf("Word: %s Translation: %s\n", translate[i].word, translate[i].translation);
}

Answer 2

Found it out:

const char *Translate[] = {
    "foo",  "bar",
    "the",  "teh",
    "what", "wut"
};

int t_idx(char *s)
{
    int i;
    for (i = 0; Translate[i]; i += 2)
        if (!strcmp(Translate[i], s))
            return i+1;

    return -1;
}

const char *translate(char *s)
{
    int idx = t_idx(s);

    return (idx == -1) ? s : Translate[idx];
}

Return values of translate:

translate("what") = "wut"
translate("some") = "some"
translate("foo")  = "bar"

Answer 3

There are no map or associative array types in standard C; you must implement it yourself. A simple idea would be to use a struct:

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

struct map {
  struct map_elem {
    char *key;
    char *value;
  } * elem;
  size_t size;
};

int main(void) {
  struct map_elem map_elem[] = {
      {"foo", "bar"}, {"the", "teh"}, {"what", "wut"}};

  struct map const map = {map_elem, sizeof map_elem / sizeof *map_elem};

  char input[] = "foo";

  for (size_t i = 0; i < map.size; i++) {
    struct map_elem *elem = map.elem + i;
    if (strcmp(input, elem->key) == 0) {
      puts(elem->value);
      break;
    }
  }
}

Of course, it's just a little example.