copying a pointers value
Author
hi
i have a function that has to be layed out the following way:
ReadFile(void *buffer)
{
fread(buffer,4,1,infile);
}
The problem is that i need to do this:
buffer = ~buffer;
but the "void" doesnt allow it. I cannot change it to char or anything as the varibale types that pass into the function MUST remain the same.
i tried doing this:
char tempbuf;
fread(tempbuf,4,1,infile);
tempbuf = ~tempbuf;
buffer = &tempbuf
.... but it compiles but when i run it there are runtime errors.
thanks for any help/advice.
cheers
Paul.
Doing it the ugly way...
union {
void* vptr;
int i;
}u;
u.vptr = NULL;
u.i = ~u.i;
//u.vptr holds what you want
union {
void* vptr;
int i;
}u;
u.vptr = NULL;
u.i = ~u.i;
//u.vptr holds what you want
You know what you doing?
I wouldn't inverse the bits in a pointer unless I did it twice to nullify the effect. You probably want to inverse the bits in the data you've read, right? Then don't hesitate to use the dereferencing operator *
zig
[edited by - civguy on January 22, 2003 12:30:56 PM]
I wouldn't inverse the bits in a pointer unless I did it twice to nullify the effect. You probably want to inverse the bits in the data you've read, right? Then don't hesitate to use the dereferencing operator *
void ReadFile(void *buffer){ fread(buffer,4,1,infile); assert(sizeof(int)==4); //since we read 4 bytes.. int* temp = reinterpret_cast<int*>(buffer); *temp = ~(*temp);} zig
[edited by - civguy on January 22, 2003 12:30:56 PM]
Author
at the end of the function, "buffer" must equal ~ of the original one...
ie: 0110011 read from file.... into varibale "buffer"
at end of function "buffer" must equal 1001100
cheers
Paul
ie: 0110011 read from file.... into varibale "buffer"
at end of function "buffer" must equal 1001100
cheers
Paul
ReadFile(void *buffer)
{
fread(buffer,4,1,infile);
unsigned int Integer = *(unsigned int *)buffer;
Integer = ~Integer;
Thats what you want. You dont'' want to inverse the pointer (buffer) you want to inverse what the pointer points to (*buffer).
{
fread(buffer,4,1,infile);
unsigned int Integer = *(unsigned int *)buffer;
Integer = ~Integer;
Thats what you want. You dont'' want to inverse the pointer (buffer) you want to inverse what the pointer points to (*buffer).
The data is not read into variable buffer. The buffer points to that data. Read my earlier reply and try it out
[edited by - civguy on January 22, 2003 12:59:44 PM]
[edited by - civguy on January 22, 2003 12:59:44 PM]
buffer is a pointer to an object of unknown type. If you reverse its bits, it''s not going to be a pointer to correct memory anymore... unless youre extremely lucky.
However, changing the memory pointed to by buffer is possible.
Your fread arguments tell me you''re reading a long integer (4 bytes), so you might consider a cast, like this :
*(unsigned long *)buffer = ~(*(unsigned long*)buffer));
ToohrVyk
-------------
Extatica - a free 3d game engine
Available soon!
Click here to learn more
However, changing the memory pointed to by buffer is possible.
Your fread arguments tell me you''re reading a long integer (4 bytes), so you might consider a cast, like this :
*(unsigned long *)buffer = ~(*(unsigned long*)buffer));
ToohrVyk
-------------
Extatica - a free 3d game engine
Available soon!
Click here to learn more
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