CODEWITHSUNDEEP
carraysstring
martinkunev
martinkunev

Reputation: 1405

C Array of strings

I want to create an array of strings. The problem is that I want to be able to access the length of each string statically. I tried this:

char *a[] = {"foo", "foobar"};

The array works fine except that I want to know the length of each element statically. I can't use sizeof(a[0]) because it returns the size of the char * pointer. What I want is the length of the size of the string (4 for a[0], 7 for a[1]).

Is there any way to do this?

Upvotes: 5

Views: 3490

Answers (7)

Cesar Najera
Cesar Najera

Reputation: 83

Maybe you could start with something like this: 

size1 = abs(a[0] - a[1]);

That will give you the difference between the beginning address of the first string and the beginning address of the second string. Therefore the size of the first string.

Then you could use some loop and array to get all the sizes.

It is not statically but maybe you could try it.

Upvotes: 0

Fred Foo
Fred Foo

Reputation: 363807

The only safe way to know the length of strings statically is to declare them all individually.

char foo[] = "foo";
char foobar[] = "foobar";

char *a[] = {foo, foobar};

You might be able to use a macro to eliminate some of the drudgery, depending on the strings' contents. sizeof(a[0]) will still be sizeof(char*), though.

Upvotes: 3

pmg
pmg

Reputation: 108988

Depending on your definition of "string", a is not an array of strings: it is an array of pointers (I define "string" as array of N characters including a null terminator).

If you want an array of lengths and strings (each capable of holding 999 characters and the null terminator), you may do something like

struct lenstring { size_t len; char data[1000]; };
struct lenstring a[] = {
      { sizeof "foo" - 1, "foo" },
      { sizeof "foobar" - 1, "foobar" },
};

Example with simplifying macro running at ideone

Upvotes: 4

Stuti
Stuti

Reputation: 1638

if you use char*a[] = {"foo", ...} style of decleration, then you can use strlen(a[0]), strlen(a[1]) etc to find the length of each string.

Upvotes: 0

Chris Lutz
Chris Lutz

Reputation: 75439

You can't. sizeof doesn't return the length of the string, but the size of the array, which in your second case is much larger than the length of the string. You need to use strlen or, perhaps, a more featured string type:

struct {
  size_t len;
  char data[]; 
} string;

But it'd be a bit more complicated to make an array of them in that case.

Upvotes: 1

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272687

In short, no, not at compile-time (at least not for an arbitrary number of strings). There are various run-time initialization-like things you can do, as others have pointed out. And there are solutions for a fixed number of strings, as others have pointed out.

The type of a[0] must be the same as that of a[1] (obviously). So sizeof() must evaluate to the same for all values of a[i].

Upvotes: 4

stacker
stacker

Reputation: 68992

You can't statically initialize a data structure with the result of strlen(), you could loop over your strings and store the string length in an initialization function.

Upvotes: 1

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