Question

How to combine 2 arrays of structs (as a map) into a third array in C

Answer 1

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

#define MAX_SIZE 64

typedef struct {
    char key[16];
    char value[32];
} MapEntry;

MapEntry map1[MAX_SIZE] = {
    {"A", "aaa"},
    {"B", "bbb"}
};
int size1 = 2;

MapEntry map2[MAX_SIZE] = {
    {"C", "ccc"},
    {"B", "XYZ"},  // Overwrites key "B"
    {"B", "XYZ"} 
};
int size2 = 2;

MapEntry combined[MAX_SIZE];
int size_combined = 0;

// Function to find index of a key in combined
int findKeyIndex(const char *key) {
    for (int i = 0; i < size_combined; i++) {
        if (strcmp(combined[i].key, key) == 0)
            return i;
    }
    return -1;
}

void combineMaps() {
    // Copy map1 into combined
    for (int i = 0; i < size1; i++) {
        strcpy(combined[size_combined].key, map1[i].key);
        strcpy(combined[size_combined].value, map1[i].value);
        size_combined++;
    }

    // Merge map2 into combined, overwriting duplicates
    for (int i = 0; i < size2; i++) {
        int index = findKeyIndex(map2[i].key);
        if (index != -1) {
            // Overwrite existing value
            strcpy(combined[index].value, map2[i].value);
        } else {
            // Add new entry
            strcpy(combined[size_combined].key, map2[i].key);
            strcpy(combined[size_combined].value, map2[i].value);
            size_combined++;
        }
    }
}

void printMap(MapEntry map[], int size) {
    for (int i = 0; i < size; i++) {
        printf("%s => %s\n", map[i].key, map[i].value);
    }
}

int main() {
    combineMaps();
    printf("Combined Arrays:\n");
    printMap(combined, size_combined);
    
    return 0;
}




/*
run:

Combined Arrays:
A => aaa
B => XYZ
C => ccc

*/

 

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