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I am trying to reassign a pointer to a 3-dimensional array.

include <stdio.h>

int main()
{
int type;

char database_of_names[3][50][16];
char database_of_suffixes[10][50][16];

char (*databaseP)[][50][16];

...

if(type == 0)
    (*databaseP)[][50][16] = &database_of_names; // Runtime error
else if(type ==1)
    (*databaseP)[][50][16] = &database_of_suffixes; // Runtime error

...

return 0;
}

I can initialize the pointer at the point of declaration like this:

char (*databaseP)[][50][16] = &database_of_names; // works

but I want to be able to switch the assignment. How can I do this by changing to above code?

Thanks

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3
  • 2
    You appear to be in the need of reading a good beginner C book, especially one that explains pointers well. Commented Dec 15, 2013 at 17:25
  • @H2CO3; Partially agreed. This question confused me at first glance. Commented Dec 15, 2013 at 17:27
  • 1
    @haccks But then you figured it out. "Confuses me at first glance" is not the same as "I have no idea what I am doing here" :P Commented Dec 15, 2013 at 17:37

4 Answers 4

Reset to default
2

Change 

(*databaseP)[][50][16] = &database_of_names;

to 

databaseP = &database_of_names;
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Comments

1

I am trying to reassign a pointer to a 3-dimensional array.

Then reassign the pointer, not the random memory space it points to (since it's uninitialized). You don't need to dereference it.

databaseP = &database_of_names;

is more than enough.

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1

With

(*databaseP)[][50][16] = &database_of_names

you first dereference the pointer, then try to index it. Don't do that, just assign the pointer:

databaseP = &database_of_names;
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1

Although the change in the other answers will make the code you have shown compile, what you probably want is to change the definition of databaseP to:

char (*databaseP)[50][16];

and the assignments of databaseP to :

if (type == 0)
    databaseP = database_of_names;
else if (type ==1)
    databaseP = database_of_suffixes;

The reason for this is that, although the changes suggested in the other answers would indeed set databaseP to point to database_of_names or database_of_suffixes, it would be a pointer to those arrays. This means you would have to use it with an extra dereference operator, as in:

… (*databaseP)[i][j][k] …

However, in C, it is usually more convenient to point the first element of an array rather than the array itself. In this case, the first element of the three-dimensional arrays is a two-dimensional array. The code I showed above defines databaseP to be a pointer to a two-dimensional array and assigns it correctly for that. The result is you can use databaseP more simply, as in:

… databaseP[i][j][k] …

Incidentally, the messages you were getting on the statements shown with “Runtime error” in your question were actually compile-time errors. They occurred when your program was compiled, not when it was run.

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1 Comment

Thanks for that explanation. Yes that is a cleaner code. Thanks!(p.s. why are there so many geek snobs in SO, why the -1 vote. Yes I have already researched this question. BTW if everyone researched all their questions %100 there would really be no need for SO huh.)

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