Programming C dynamic table error storage size of `table' isn't known

Question

I want to compile the program with a dynamic size of the table I tried int Table[]; My program's

the compiler returns this message 4 C:\Documents and Settings\Administrateur\Mes documents\TD4.c storage size of `table' aren't known? I don't know storage? what is my fault

Your fault is that you don't know which programming language you use: is it C or C++? Please adjust your tags appropriately and/or name your documents the way you need it. — glglgl, Dec 27 '12 at 19:38
before, at the university, we use cpp extension to compile a c program . — Zouhair Kasmi, May 13 '19 at 16:12

score 4 · Accepted Answer · answered Dec 27 '12 at 19:34

4

In C, you can't declare an array with unknown size.

int Table[];

is simply not allowed.

Instead you can declare a pointer:

int *Table;

and dynamically allocate/reallocate using malloc/realloc functions.

answered Dec 27 '12 at 19:34

P.P

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You can declare array in that case. `int table[100];` Note that it can't a variable like `N`. Variable length arrays are supported only after C99. But `N` can be defined `#define N 100`. – P.P Dec 27 '12 at 20:13

score 1 · Answer 2 · answered Dec 27 '12 at 19:34

1

When you a table you have to declare it's initial size: int table[SIZE];. When you don't know the table's size at compilation time (e.g. you read data from the user) you always can allocate memory in different way (size is a variable, not a constant):

int* table = (int*)malloc(sizeof(int)*size));

answered Dec 27 '12 at 19:34

Adam Sznajder

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Don't cast the return value of `malloc` in C. – netcoder Dec 27 '12 at 20:25
Hmm... why? Could I do this in C++? – Adam Sznajder Dec 27 '12 at 20:38
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In C++ you have to. In C, [you must not](http://stackoverflow.com/questions/1565496/specifically-whats-dangerous-about-casting-the-result-of-malloc). – netcoder Dec 27 '12 at 20:42

score 1 · Answer 3 · answered Dec 27 '12 at 19:35

1

If you want to create a dynamic Table/array, you can do so using malloc function in C and using new operator in C++. You should deallocate the memory using free and delete depending on whether you use C or C++.

answered Dec 27 '12 at 19:35

Recker

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I can see that warning is thrown out from .cpp file. Thats why I am mentioning C++. – Recker Dec 27 '12 at 19:36

score 1 · Answer 4 · answered Dec 27 '12 at 19:38

You cannot dynamically define an array in that way. You must give it a storage size:

    int Table[43];

Another way would be to use malloc:

    int *Table = malloc (sizeof (int) * N);
    int i;

    for (i = 0; i < N; i++)
        Table[i] = i;

Where N would be passed by some means. Don't forget to use free() on the array after.

Programming C dynamic table error storage size of `table' isn't known

4 Answers4