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Without free(), bound control and etc, it's sample, yes

maper.c

/*
 * Copyright 2021 Oleg Borodin  <borodin@unix7.org>
 */
 
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#define TYPE_STR 1
#define TYPE_INT 2
 
typedef struct {
    char*   key;
    int     type;
    union {
        char**  cref;
        int*    iref;
    };
} record_t;
 
typedef struct {
    record_t **records;
    size_t size;
    size_t cap;
} maper_t;
 
record_t* new_record(char* key, int type, void* val) {
    record_t *record = malloc(sizeof(record_t));
    record->key = key;
    record->type = type;
    switch (type) {
         case TYPE_STR:
             record->cref = val;
             break;
         case TYPE_INT:
             record->iref = val;
             break;
    }
    return record;
}
 
maper_t* new_maper() {
    maper_t* maper = malloc(sizeof(maper_t));
    maper->cap = 100;
    maper->size = 0;
    maper->records = malloc(sizeof(record_t*) * maper->cap);
    return maper;
}
 
void maper_add(maper_t *maper, record_t* record) {
    maper->records[maper->size++] = record;
}
 
record_t* maper_find(maper_t* maper, char* key) {
    for (int i = 0; i < maper->size; i++) {
        if (strcmp(maper->records[i]->key, key) == 0) {
            return maper->records[i];
        }
    }
    return NULL;
}
 
void maper_set(maper_t* maper, char* key, char* val) {
    for (int i = 0; i < maper->size; i++) {
        if (strcmp(maper->records[i]->key, key) == 0) {
            printf("key %d %s %s\n", i, key, val);
            int n = 0;
            switch (maper->records[i]->type) {
                 case TYPE_STR:
                    *(maper->records[i]->cref) = val;
                    break;
                 case TYPE_INT:
                    n = strtol(val, NULL, 10);
                    *(maper->records[i]->iref) = n;
                    break;
 
            }
        }
    }
}
 
typedef struct {
    char* elem1;
    char* elem2;
    int elem3;
} test_t;
 
int main(int argc, char **argv) {
 
    test_t t;
 
    maper_t* maper = new_maper();
    maper_add(maper, new_record("key1", TYPE_STR, &(t.elem1)));
    maper_add(maper, new_record("key2", TYPE_STR, &(t.elem2)));
    maper_add(maper, new_record("key3", TYPE_INT, &(t.elem3)));
 
    maper_set(maper, "key1", "val1");
    maper_set(maper, "key2", "val2");
    maper_set(maper, "key3", "123");
    printf("%s %s %d\n", t.elem1, t.elem2, t.elem3);
 
    return 0;
}

$ cc -Wall -o maper maper.c

$ ./maper
key 0 key1 val1
key 1 key2 val2
key 2 key3 123
val1 val2 123