#include <stdio.h>

typedef struct file_t {
    char *name;
    FILE *file;
    char *(*read)(File*);
    long int (*size)(File*);
} File;

long int file_t__size(File *this) {
    fseek(this->file, 0, SEEK_END);
    long int fsize = ftell();
    rewind(this->file);
    return fsize;
}
char *file_t__read(File *this) {
    long int fsize = this->size(this);
    char *buff = malloc(fsize + 1);
    buff[fsize] = '\0';
    long int rsize = fread(buff, 1, fsize, this->file);
    if(rsize != fsize) {
        free(buff);
        return NULL;
    }
    return buff;
}

file_t open_file(char *fname) {
    return (File) {
        fname,
        fopen(fname, "r"),
        &file_t__read,
        &file_t__size
    };
}

int main() {
    char *fname = malloc(1024);
    printf("Enter file name (max. 1024 chars): ");
    scanf("%s1024", fname);
    File file = open_file(fname);
    return 0;
}