Question

How to get the country name from the 2-letter country code (alpha-2) in C

Answer 1

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

/* ------------------------------------------------------------
   CountryEntry
   Represents a single ISO alpha‑2 → country name mapping.
   ------------------------------------------------------------ */
typedef struct {
    const char *code;
    const char *name;
} CountryEntry;

/* ------------------------------------------------------------
   A sorted lookup table for fast binary search.
   Add more entries as needed, but keep it sorted by code.
   ------------------------------------------------------------ */
static const CountryEntry COUNTRY_TABLE[] = {
    {"CA", "Canada"},
    {"CN", "China"},
    {"DE", "Germany"},
    {"FR", "France"},
    {"GB", "United Kingdom"},
    {"IN", "India"},
    {"JP", "Japan"},
    {"US", "United States"}
};

static const size_t COUNTRY_COUNT = sizeof(COUNTRY_TABLE) / sizeof(CountryEntry);

/* ------------------------------------------------------------
   normalizeCode
   Converts a 2‑letter code to uppercase for consistent matching.
   ------------------------------------------------------------ */
void normalizeCode(char *code) {
    for (size_t i = 0; code[i] != '\0'; ++i) {
        code[i] = (char)toupper((unsigned char)code[i]);
    }
}

/* ------------------------------------------------------------
   getCountryName
   Performs a binary search on the sorted table.
   Returns NULL if the code is not found.
   ------------------------------------------------------------ */
const char* getCountryName(const char *alpha2) {
    char code[3];
    strncpy(code, alpha2, 2);
    code[2] = '\0';

    normalizeCode(code);

    size_t left = 0;
    size_t right = COUNTRY_COUNT;

    while (left < right) {
        size_t mid = left + (right - left) / 2;
        int cmp = strcmp(code, COUNTRY_TABLE[mid].code);

        if (cmp == 0) {
            return COUNTRY_TABLE[mid].name;
        } else if (cmp < 0) {
            right = mid;
        } else {
            left = mid + 1;
        }
    }

    return NULL;
}

/* ------------------------------------------------------------
   main
   Demonstrates the lookup function with several sample codes.
   ------------------------------------------------------------ */
int main(void) {
    const char *codes[] = {"US", "GB", "FR", "JP", "ZZ"};
    const size_t count = sizeof(codes) / sizeof(codes[0]);

    for (size_t i = 0; i < count; ++i) {
        const char *name = getCountryName(codes[i]);

        if (name) {
            printf("%s → %s\n", codes[i], name);
        } else {
            printf("%s → (invalid code)\n", codes[i]);
        }
    }

    return 0;
}


/*
run:

US → United States
GB → United Kingdom
FR → France
JP → Japan
ZZ → (invalid code)

*/

 

70+ SQL courses for beginners and professionals