#include <stdio.h>

int main(int argc, char *argv[])
{
    char x[4] = "123";
    char y[4] = "abc";
    FILE *f = fmemopen(x, 3, "r");
    FILE *g = fmemopen(y, 3, "w");
    setvbuf(f, NULL, _IONBF, 0);
    setvbuf(g, NULL, _IONBF, 0);

    fread(&x[1], 1, 2, f);
    fwrite(&y[1], 1, 2, g);
    
    printf("x = %s\n", x);
    printf("y = %s\n", y);
    
    fclose(f);
    fclose(g);

    printf("x = %s\n", x);
    printf("y = %s\n", y);
    
    return 0;
}