No names for variables?

Question

I want to be able to take input with a function but I want to store the information. Is there anyway to declare a variable that doesn't have a name and only can be accessed by a pointer?

something like this:

float* = float NULL 5;

Thanks.

EDITED: What I needed to do was to have an infinite amount of arrays that store a very large amount of ints. However, I am loading all this data from files and I need to access it from many other classes. I know how many times the function is run so i can keep them in an array but I don't know how many ints are or potentially are loaded

So the pointers son't need to have names because they will be stored in an array to be used later. I just wanted to be able to create global variables multiple times and just access them from an array.

lets say `float* = float NULL 5;` is valid. how would you think the access to this pointer will look like ? — Roee Gavirel, Nov 06 '12 at 13:03
I'd be interested to know, what would the advantage be to this in your mind? — Mike, Nov 06 '12 at 13:11
Actually, there is a way, in which it can indeed be done. Is it possible to reopen the question, so that i can add an answer? — anishsane, Nov 06 '12 at 23:38
@anishsane I don't believe so. But I figured out how to do what I wanted anyways. thanks. — BlueSpud, Nov 08 '12 at 00:10

score 2 · Answer 1 · answered Nov 06 '12 at 13:03

2

The answer is NO. You have to have memory allocated for the variable.

Either the function (that returns value) should allocate memory, or your caller function.

But what you are trying to do is not even fitting C syntax.

answered Nov 06 '12 at 13:03

anishsane

20,270
5
40
73

What about compound literals and construction like float* ptr = (float[]){5}? – codewarrior Nov 06 '12 at 13:16
@codewarrior: In that case, the memory allocated is read only memory; in const segment. But memory is allocated & pointer points to a valid location. – anishsane Nov 06 '12 at 13:18
I would only like to answer the question: "Is there anyway to declare a variable that doesn't have a name and only can be accessed by a pointer?" - in this case there is! – codewarrior Nov 06 '12 at 13:24
Then `malloc` is also a possible answer? – anishsane Nov 06 '12 at 13:26
In that sense YES. You have variable without name and can access it using pointer. – codewarrior Nov 06 '12 at 13:28

score 0 · Answer 2 · answered Nov 06 '12 at 13:02

Well, you can allocate new memory from the heap with malloc(), and store stuff in there. That is probably what you want, the function can then return the pointer and hand it over to other functions. When the data is no longer needed, it should be de-allocated with free().

score 0 · Answer 3 · answered Nov 06 '12 at 13:02

0

The simple answer is NO! So why do you want to do this daft thing?

answered Nov 06 '12 at 13:02

Ed Heal

59,252
17
87
127

What I needed to do was to have an infinite amount of arrays that store a very large amount of ints. However, I am loading all this data from files and I need to access it from many other classes. I know how many times the function is run so i can keep them in an array but I don't know how many ints are or potentially are loaded – – BlueSpud Nov 06 '12 at 13:32

score 0 · Answer 4 · answered Nov 06 '12 at 13:03

0

No. You could invent a name that you're not using otherwise:

 float myFloatINTERNAL_DONTUSE;
 float * const myFloat = &myFloatINTERNAL_DONTUSE;

but what for? Just declare an ordinary local variable and use the & operator when you need its address.

answered Nov 06 '12 at 13:03

hmakholm left over Monica

23,074
3
51
73

score 0 · Answer 5 · answered Nov 06 '12 at 13:03

0

Yes you can.

float* p = malloc(sizeof(*p));

You nave a named pointer variable p, but the object it points to has no name. Don't forget to free the memory later.

answered Nov 06 '12 at 13:03

Armen Tsirunyan

130,161
59
324
434

He does not want any name for pointer either, I think... – anishsane Nov 06 '12 at 13:04
@anishane: Why do you think so? – Armen Tsirunyan Nov 06 '12 at 13:04
From whatever snippet he has posted... – anishsane Nov 06 '12 at 13:05
3

@anishsane: His snippet made ZERO sense to me, so I chose to ignore it and instead answer his textual question – Armen Tsirunyan Nov 06 '12 at 13:05
[Do not cast the return of malloc](http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc) and I usually advice to use `sizeof(*p)` so you won't have to change anything anytime (and this goes for any type of p) – Eregrith Nov 06 '12 at 13:07
he he... your comment about his snippet makes sense :D – anishsane Nov 06 '12 at 13:07
@Eregrith: Point taken... I'm a bit rusty in C, I am more of a C++ guy :) – Armen Tsirunyan Nov 06 '12 at 13:08
With gcc at least, you can cast it with `p=(typeof(p))malloc(sizeof(*p));` typeof works with gcc. – anishsane Nov 06 '12 at 13:09
@anishane: The cast T*->void* is implicit in C, unlike C++ – Armen Tsirunyan Nov 06 '12 at 13:10
Btw... Is there decltype in C99? – Armen Tsirunyan Nov 06 '12 at 13:10

score 0 · Answer 6 · answered Nov 06 '12 at 13:04

No, C standart (so obviously your compiler too) doesn't support a variables without names. When you declare a pointer om something, you must give it a name too.
Well, what you want to do there, reasonably, is to create a variable in heap and then access it by a pointer with name:

float * const ptr = malloc(sizeof(float));

That's it, so here you go.

score 0 · Answer 7 · answered Nov 06 '12 at 13:06

0

Suppose, there had been a way, to do it,

How would you access the variable without using a name?

Even pointer is a "named pointer variable" :-)

answered Nov 06 '12 at 13:06

anishsane

20,270
5
40
73

What I needed to do was to have an infinite amount of arrays that store a very large amount of ints. However, I am loading all this data from files and I need to access it from many other classes. I know how many times the function is run so i can keep them in an array but I don't know how many ints are or potentially are loaded – BlueSpud Nov 06 '12 at 13:32
Then create a linked list? We can later optimize in terms of memory in case this is the desired solution. (linked list need additional memory for next pointer & would be costly, if data is 4 bytes int & next is also 4 byte ptr) – anishsane Nov 06 '12 at 13:35
Yes. load a bunch of files. put them all in an array and do something to all of them. get rid of them. – BlueSpud Nov 06 '12 at 13:40

codewarrior · Answer 8 · 2012-11-06T13:17:36.853

0

Besides dynamically allocated objects (created using malloc) there are also supported from C99 compound literals.

E.g. construction like below

char **foo = (char *[]) { "x", "y", "z" };

or for your purposes

float *ptr = (float[]){5};

construct an array and actually you have only pointer to it without having object name itself.

edited Nov 06 '12 at 13:17

answered Nov 06 '12 at 13:08

codewarrior

1,269
1
9
14

No names for variables?

8 Answers8