How to initialize char arrays for a struct outside using strings?

Question

I'm trying to make a function that auto populates data into a binary file if the file does not exist. Since it doesn't exist, I want to add data myself from a function so it can also create the file itself with the data.

The struct I made

struct Address {
    char city[ADDR_SIZE];
    char state[ADDR_SIZE];
    int zipcode;
};
struct Record {
    char name[NAME_SIZE];
    int socialSecurityNum;
    int dateOfBirth;
    Address address;
};

I'm trying to add the data like this

dataFile.seekp(getBytePosition(0), ios::beg);
citizen.name = "Some name"; //ERROR: char[30] not assignable
citizen.socialSecurityNum = 123123123;
citizen.address.zipcode = 75042;
dataFile.write(reinterpret_cast<char *>(&citizen), sizeof(citizen));

Giving it integers is simple, but how do I make it populate the char name array?

I also tried these but failed

citizen.name[NAME_SIZE] = "Some name"; //Fails
citizen.name[NAME_SIZE] = {"Some Name"}; //Fails
citizen.name[NAME_SIZE] = 'Some Name'; //Too Many errors

Dimitrios Bouzas · Accepted Answer · 2015-10-08 06:32:27Z

3

First option (not recommended): Use strcpy

strcpy(citizen.name, "Some name");

or the more safer (recomended) strncpy

strncpy(citizen.name, "Some name", sizeof(citizen.name));

Second option (recomended): Instead of char array use a std::string:

struct Address {
    std::string city;
    std::string state;
    int zipcode;
};
struct Record {
    std::string name;
    int socialSecurityNum;
    int dateOfBirth;
    Address address;
};

With std::string you can assign to it:

citizen.name = "Some name";

However you'll have the additional burden of serializing your data but I believe it worths it.

edited Oct 8, 2015 at 6:32

answered Oct 8, 2015 at 6:12

Dimitrios Bouzas

43.1k11 gold badges103 silver badges177 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Jozey Over a year ago

What's wrong with strcpy? If I remember, I did try them as strings first, but then I had to use cin.getline to write to a binary file and I believe I was getting errors. I've come a long way since and it would take a while to switch it all back to string.

Remy Lebeau Over a year ago

@Jozemite:Apps: strcpy() does not perform bounds checking so can cause buffer overflows if used incorrectly. Use strncpy() or equivalent instead.

Remy Lebeau Over a year ago

@101010: The use of std::string is fine for manipulating data in memory, but if you put a std::string in a struct, you can no longer write that struct as-is to a file, or read it back. You have to serialize the data into a flat format instead. That is more work. Using a fixed array allows for direct file I/O.

Dimitrios Bouzas Over a year ago

@JozemiteApps Well if you're careful there's nothing wrong. The problem is that using char arrays and their C facilities could cause buffer overflows. Using std::string is the recommend way to store and manipulate strings, unless you're programming in a very strict environment in terms of hardware resources.

Dimitrios Bouzas Over a year ago

@RemyLebeau Yes that's true. Nevertheless, I believe it worths the trouble.

|

marom · Accepted Answer · 2015-10-08 06:13:05Z

1

Use strcpy

strcpy(citizen.name, "Some name") ;

Use of std::string would simplyfy code but would make loading/saving to file more difficult since std::ostream.write would not be a bit more complex

answered Oct 8, 2015 at 6:13

marom

5,23813 silver badges15 bronze badges

Comments

Community · Accepted Answer · 2017-05-23 10:29:50Z

1

Try using strcpy or memcpy with the appropriate casts.

Check this.

edited May 23, 2017 at 10:29

CommunityBot

11 silver badge

answered Oct 8, 2015 at 6:14

Jerry

1,8225 gold badges21 silver badges42 bronze badges

Comments

Christophe · Accepted Answer · 2015-10-08 06:24:06Z

1

As you have a char array, you can't just assign values with =. You should use either strcpy() or better, std::copy()

edited Oct 8, 2015 at 6:24

answered Oct 8, 2015 at 6:15

Christophe

75.1k7 gold badges87 silver badges182 bronze badges

Comments

Remy Lebeau · Accepted Answer · 2015-10-08 06:27:22Z

1

You cannot assign a char* to a char[] array after the array has been declared. Use strncpy() instead to copy the content of the char* data into the char[] memory:

strncpy(citizen.name, "Some name", NAME_SIZE);

answered Oct 8, 2015 at 6:27

Remy Lebeau

609k36 gold badges516 silver badges875 bronze badges

Collectives™ on Stack Overflow

How to initialize char arrays for a struct outside using strings?

5 Answers 5

6 Comments

Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

6 Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related