Assigning char array a value in C

Question

What is the difference between:

char fast_car[15]="Bugatti";

and

char fast_car[15];
fast_car="Bugatti";

Because the second one results with compile error:

error: incompatible types when assigning to type ‘char[15]’ from type ‘char *’

While the first one works fine. Putting a string in array in different place than array initialisation would be helpful.

You can use a string function like snprintf or strncpy to fill the array with a new value — Niklas B.
– Niklas B., Commented Aug 28, 2012 at 13:25
Don't use strncpy unless you're really really really sure that's what you want. Make sure the buffer is big enough and use strcpy instead. — harald
– harald, Commented Aug 28, 2012 at 13:29
@hardpenguin, it silently truncates the string. That's very rarely what you want. In addition when truncating it does not terminate the string. See for instance here. — harald
– harald, Commented Aug 28, 2012 at 13:37
@harald: strncpy definitely is not worse than strcpy safety-wise. Of course you have to be sure about what you do in both cases. — Niklas B.
– Niklas B., Commented Aug 28, 2012 at 13:40
@harald: In many cases, a truncated string is better than a buffer overflow (provided that you properly set the terminating null byte). How many security-critical bugs do you know that are the result of a truncated string? Of course it's even better to not introduce bugs at all, but we all know that this is not going to happen. The real solution is using a better string library than the C stdlib. — Niklas B.
– Niklas B., Commented Aug 28, 2012 at 13:58

cnicutar · Accepted Answer · 2012-08-28 13:24:10Z

9

The first is an initialization while the second is an assignment. Since arrays aren't modifiable values in C you can't assign new values to them.

Mind you, you can modify array contents, you just can't say fast_car = .... So the contents are modifiable, the arrays themselves are not.

Using the same symbol = for these widely different concepts is of debatable value.

answered Aug 28, 2012 at 13:24

cnicutar

184k26 gold badges378 silver badges398 bronze badges

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

6 Comments

Nick Brunt Over a year ago

str_replace("modifiable", "mutable"); ;)

Niklas B. Over a year ago

@Nick: String substitution is actually not that simple in C ;)

hardpenguin Over a year ago

@cnicutar , can you suggest another solution? It is about manually assigning few array variables from the structure. Using pointer to char works, but isn't it a bad solution for managing memory?

Eric Postpischil Over a year ago

Additionally, a reason that initialization can set an array to a whole string and assignment cannot is that initialization is accomplished by storing the data executable image, where it “naturally” forms a part of the program’s memory when loaded. It does not cause any run-time operations beyond loading the program. In contrast, assignment requires copy operations, and this is a more involved process than C was originally designed for.

cnicutar Over a year ago

@hardpenguin You can use strcpy, use pointers etc. Depends on the nature of the data and the processing being done.

|

Utsav T · Accepted Answer · 2015-02-20 20:09:02Z

4

char fast_car[15]="Bugatti";

It says fast_car is an array and be initialized with string the "Buratti". Correct Usage :

char fast_car[15];
fast_car="Bugatti";

The first line is a declaration of char array(not initialized). Second, fast_car here is just an address(a pointer) of the first element in this array of char. The assignment of pointer fast_car to array of char "Buratti" is incorrect by difference type of value.

edited Feb 20, 2015 at 20:09

Utsav T

1,5352 gold badges25 silver badges42 bronze badges

answered Aug 29, 2012 at 5:02

nofomopls

3434 silver badges19 bronze badges

Collectives™ on Stack Overflow

Assigning char array a value in C

2 Answers 2

6 Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

6 Comments

Comments

Linked

Related