string vs char[50]

[SRS]

While curising the C string tutorial on this site, I found a set of variables resembling my struct. Here is what I found:

  char name[50];
  char lastname[50];
  char fullname[100];

...and here is my struct:

struct contacts
{
    string firstName;
    string lastName;
    string companyName;
    string homeAddress;
    int id_number;
    int age;
};

...and here are my questions:
1: Should I use string or the char arrays for what I am doing (storing names)
2: Why or why not? -memory use advantages, etc anything that may apply

[hk_mp5kpdw]

Yes, they are very adaptable, they can shrink or grow to accommodate whatever size data they need to so they only use enough memory to do so. Management of this memory is automatic so you don't really have to think about it too much. There may be a bit of a learning curve getting used to them and understanding the more useful of the member functions available.

[cyberfish]

from what i have read, the general rule of thumb is to use C++ strings (std::string) instead of C strings (char arrays) unless you know what you are doing, since C++ strings are better encapsulated, and is easier and safer to manipulate. The only drawback I would imagine would be that it's a bit less efficient compared to C strings, but most of the time, efficiency doesn't practically matter in string manipulation codes.

[cpjust]

Always use std::string instead of char arrays.
Always use std::vector<T> instead of arrays of T.

Arrays can't grow or shrink (unless you use new & delete [], but that can lead to bugs if you don't do it carefully).

[matsp]

There is one exception: If you want to store the data structure as a binary format in a file [1] you are better off with fixed size arrays than any C++ object type, because you can then store the entire struct with one write call, rather than as a bunch of small writes of individual strings and other "pieces".

[1] Yes, I'm fully aware that there are all kinds of problems with portability if a struct is stored in a binary file.

--
Mats

[cpjust]

There is one exception: If you want to store the data structure as a binary format in a file [1] you are better off with fixed size arrays than any C++ object type, because you can then store the entire struct with one write call, rather than as a bunch of small writes of individual strings and other "pieces".

I don't agree. You can write a whole file to a vector in one pass too.

[matsp]

I don't agree. You can write a whole file to a vector in one pass too.

You mean write a vector to a file in one pass? Perhaps, but does that work also if you have a struct of strings inside the vector? Without help from member functions or similar?

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Mats

[Cactus_Hugger]

You mean write a vector to a file in one pass? Perhaps, but does that work also if you have a struct of strings inside the vector? Without help from member functions or similar?

No, it wouldn't work with string members. (Or if it did, it's certainly not portable.)
Regardless, even with char arrays - if they represent strings, then you have to make sure that what's past the terminating null is zeroed out, or you'll be writing old string values, old RAM values, possibly sensitive and certainly not needed information to disk.

[cpjust]

You mean write a vector to a file in one pass? Perhaps, but does that work also if you have a struct of strings inside the vector? Without help from member functions or similar?

No, I mean using vector<unsigned char> to store binary file data, or vector<char> to store a text file.

[matsp]

No, it wouldn't work with string members. (Or if it did, it's certainly not portable.)
Regardless, even with char arrays - if they represent strings, then you have to make sure that what's past the terminating null is zeroed out, or you'll be writing old string values, old RAM values, possibly sensitive and certainly not needed information to disk.

True - If I write code that stores structs to files, I generally use memset() to fill with zero for this exact reason [and it's also "handy" to have all values zero anyways!]

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Mats