Malloc and data types

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Hy
Why this doesn't work:

C

int main (void) {

	int *x = NULL;

	x = malloc (sizeof(int));

	free(x);

	x = NULL;

	getchar();

	return 0;
}

It says that it cannot convert from 'void *' to 'int *'

Posted 23-Jun-11 7:27am

Member 641034

Updated 24-Jun-11 2:48am

Richard MacCutchan

v5

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CPallini 24-Jun-11 8:52am

Because you didn't read any good C programming book?

Albert Holguin 24-Jun-11 11:01am

lol, that's a good point.. if it was a good book it would explain what it's doing in the example and why...

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Richard MacCutchan · Accepted Answer · 2011-06-23T07:31:00

Solution 1

The malloc() function returns a pointer to the allocated memory as a void* which must be cast (by you) to the appropriate type. You need to change your code thus, in order to let the compiler know that you understand what you are doing:

x = (int*)malloc (sizeof(int));

[edit by AH]
The reason malloc() returns a void* is because its a generic call to allocate memory in bytes. Why generic? So it can be used to allocate memory for any type of data (characters, integers, double, structures, anything really).
[/edit]

Posted 23-Jun-11 7:31am

Richard MacCutchan

Updated 23-Jun-11 8:09am

v3

Comments

Albert Holguin 23-Jun-11 14:05pm

its that easy, my 5, added comment (hope you don't mind)

Richard MacCutchan 24-Jun-11 4:06am

Thanks for the extra comments.

Sergey Alexandrovich Kryukov 23-Jun-11 14:37pm

Yes, not too hard riddle. My 5. :-)
--SA

Richard MacCutchan 24-Jun-11 4:08am

It's quite worrying how many developers these days do not seem to have learnt (or been taught) the basics before trying to write more advanced code.

Member 641034 24-Jun-11 7:18am

Hy
Could You help me with this code that I posted?
Thanks a lot!

Richard MacCutchan 24-Jun-11 8:50am

What code? The sample above does not do anything.

Sergey Alexandrovich Kryukov 24-Jun-11 20:16pm

Hopefully not in this case; OP honestly runs through a book, with no vanity of getting anything "cool", that's good...
--SA

Member 641034 24-Jun-11 6:11am

HyI am trying to learn C from book 'C programming: Visual QuickStart Guide' by Larry Ullman and Marc Liyanage (2005.).
I was trying a sample code from the book.

Richard MacCutchan 24-Jun-11 8:51am

Without seeing the sample it's difficult to guess what your problem is.