Thread: Saving data in a struct field depending on the data introduced

There are a few ways you could go.

Code:

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

// All the values are the same type
struct Pair {
    const char *name;
    int value;
};

struct Pair example[3] = {
    { "ab", 0 },
    { "ba", 0 },
    { "ca", 0 },
};

void assign(struct Pair data[], size_t len, const char *name, int value) {
    for ( size_t i = 0 ; i < len ; i++ ) {
        if ( strcmp(data[i].name, name) == 0 ) {
            data[i].value = value;
        }
    }
}

// All the values have different types
struct Pair2 {
    const char *name;
    int         offset;
    enum {
        T_INT,
        T_DOUBLE,
        T_CHAR,
    }           type;
};

// Your data, with heterogenous types
struct Data {
    int     ab;
    double  ba;
    char    ca;
};

struct Pair2 map[3] = {
    { "ab", offsetof(struct Data,ab), T_INT },
    { "ba", offsetof(struct Data,ba), T_DOUBLE },
    { "ca", offsetof(struct Data,ca), T_CHAR },
};

void assign2(struct Pair2 map[], size_t len, const char *name, struct Data *instance, int value) {
    for ( size_t i = 0 ; i < len ; i++ ) {
        if ( strcmp(map[i].name, name) == 0 ) {
            switch ( map[i].type ) {
                case T_INT:
                {
                    int *p = (int*)((char*)instance + map[i].offset);
                    *p = value;
                    break;
                }
                case T_DOUBLE:
                {
                    double *p = (double*)((char*)instance + map[i].offset);
                    *p = value;
                    break;
                }
                case T_CHAR:
                {
                    char *p = (char*)((char*)instance + map[i].offset);
                    *p = value;
                    break;
                }
            }
        }
    }
}

int main ( ) {
    assign( example, 3, "ba", 42);
    struct Data instance;
    assign2( map, 3, "ba", &instance, 42);
    printf("%d %f\n", example[1].value, instance.ba);
}