Hi All,
I have a buffer allocation function that was declared as follows:
 int MyBuffAlloc(size_t size, void **pBuff);
I called this function
1 typedef struct MyStruct
2 {
3    int A;
4    int B;
5 } MyStruct;
6 int *pMyBuff;
7 int RetCode;
//cast int* into void*
8 RetCode = MyBuffAlloc(sizeof(MyStruct), &((void *)(pBuff)));
......

My compiler didn't complain about the call in line 8. But when I run
a lint on this file, the lint complained:
Error 50: Attempted to take the address of a non-lvalue.
I made a cast so that I could call function MyBuffAlloc properly. When
I removed the cast I got no error from neither the compiler nor lint.
My question is: Why I got an error when trying to be syntactically
correct, and didn't get an error the other way around?
Thanks.

Sent via Deja.com
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The result of a cast is not an lvalue.  The & operator must have
an lvalue as its argument.

Are you sure?  void ** is not compatible with int **.  What
compiler are you using?

You should have received an error both ways.
--
"I hope, some day, to learn to read.
 It seems to be even harder than writing."
--Richard Heathfield

I think you want line 8 to read:
  RetCode = MyBuffAlloc(sizeof(MyStruct), (void **)&pBuff);

Or if the function prototype is in scope, it can take care of the casting:
  RetCode = MyBuffAlloc(sizeof(MyStruct), &pBuff);

BTW, you declare pMyBuff to be a pointer to an int......shouldn't it be a
pointer to a MyStruct?

~Glynne

Hi All,
I have a buffer allocation function that was declared as follows:
 int MyBuffAlloc(size_t size, void **pBuff);
I called this function
1 typedef struct MyStruct
2 {
3    int A;
4    int B;
5 } MyStruct;
6 int *pMyBuff;
7 int RetCode;
//cast int* into void*
8 RetCode = MyBuffAlloc(sizeof(MyStruct), &((void *)(pBuff)));
......

My compiler didn't complain about the call in line 8. But when I run
a lint on this file, the lint complained:
Error 50: Attempted to take the address of a non-lvalue.
I made a cast so that I could call function MyBuffAlloc properly. When
I removed the cast I got no error from neither the compiler nor lint.
My question is: Why I got an error when trying to be syntactically
correct, and didn't get an error the other way around?
Thanks.

Sent via Deja.com
http://www.deja.com/

Thanks for the answer. I'm using CAD-UL CXX386 C++ Cross Optimizing
Compiler.

Sent via Deja.com
http://www.deja.com/

This type of interface is a sign of trouble. You cannot use the type void ** as
a generic pointer-to-any-pointer. This issue is covered in the comp.lang.c FAQ.

The result of a cast expression is not an lvalue and so has no address.
The expression (void *) pBuff means to convert the lvalue pBuff into
the value stored in the object that it designates, and then to convert
that value to (void *). By the time this happens, the lvalue property
has been stripped away.

Your compiler is broken or is being operated in some non-conforming mode in
which it is possible for the results of cast expressions to behave as lvalues.
Find out how to make your compiler conform to ANSI C as closely as it can. In
the case of the GNU C compiler, for instance, the -ansi -pedantic options do
this.

On Mon, 25 Dec 2000 23:14:24 GMT, "Glynne"

That won't cure anything. void** is not some kind of generic pointer.

The compiler should start complaining if there is a prototype in
scope. You can not implicitly convert some pointer to void**.

Bart v Ingen Schenau
--
FAQ for clc: http://www.eskimo.com/~scs/C-faq/top.html