Segmentation fault on loading structure from file in C - c++

Question

I was playing with C/'s fopen() and putc() functions and wanted to implement serialization/deserialization of a structure. However, here some "Segmentation fault" error occurs. I investigated similar questions and found, that it happens when I am trying to access some memory that doesn't belong to me.
What should I fix in my code to make it work properly?
struct Account {
string holder_name;
string holder_password;
double current_sum;
};
int save_to_file(Account * account);
Account * load_from_file(string holder_name);
int main(){
Account account = { "BEN", "password", 200.0 };
save_to_file(&account);
load_from_file("BEN");
return 0;
}
int save_to_file(Account * account){
const char * cstr = account->holder_name.c_str();
int size = sizeof(struct Account);
FILE * fp = fopen(cstr, "wb");
char * c;
c = (char *) account;
for(int i=0; i < size; i++)
{
putc(*c++, fp);
}
return fclose(fp);
}
Account * load_from_file(string holder_name)
{
FILE * fp;
char *c;
int i;
int size = sizeof(struct Account);
struct Account * ptr = (struct Account *) malloc(sizeof(struct Account));
if ((fp = fopen(holder_name.c_str(), "rb")) == NULL)
{
perror("Error occured while opening file");
return NULL;
}
c = (char *)ptr;
while ((i = getc(fp))!=EOF)
{
*c = i;
c++;
}
fclose(fp);
return ptr;
}

Answer 1

The string type doesn't belongs to C language, it's a object that comes from C++.
Since it may be implemented with pointers inside the object, you can't simply write their binary values to a file : the pointed memory won't be allocated when you'll read the file later.
A simple rule is that writing a pointer value to a file is a probably a mistake.
For your code to work, simply replace the string type with a char []. Here is the code with this only modification :
#include <stdlib.h>
#include <stdio.h>
struct Account {
char holder_name[100];
char holder_password[100];
double current_sum;
};
int save_to_file(struct Account * account);
struct Account * load_from_file(char *holder_name);
int main(){
struct Account account = { "BEN", "password", 200.0 };
save_to_file(&account);
load_from_file("BEN");
return 0;
}
int save_to_file(struct Account * account){
const char * cstr = account->holder_name;
int size = sizeof(struct Account);
FILE * fp = fopen(cstr, "wb");
char * c;
c = (char *) account;
for(int i=0; i < size; i++)
{
putc(*c++, fp);
}
return fclose(fp);
}
struct Account * load_from_file(char *holder_name)
{
FILE * fp;
char *c;
int i;
int size = sizeof(struct Account);
struct Account * ptr = (struct Account *) malloc(sizeof(struct Account));
if ((fp = fopen(holder_name, "rb")) == NULL)
{
perror("Error occured while opening file");
return NULL;
}
c = (char *)ptr;
while ((i = getc(fp))!=EOF)
{
*c = i;
c++;
}
fclose(fp);
return ptr;
}