trouble with pointers

**lucaspewkas** · 05-20-2005

OK once again, pointers are causing me headaches

I'm trying to get a word from a file, and write that into a buffer. The buffer is malloced like so:

Code:

char *buf = malloc( INIT * sizeof(char) );

and the function called:

Code:

while ( getword(buf, INIT) != EOF )

where getword has the definition:

Code:

int
getword(char *W, int size)

Then the buffer is realloced inside the getword function, if necessary.

Code:

size *= 2;
W = realloc(W, size * sizeof(char) );

The problem is, if the realloc is done, the W returned is correct, but the buf recieved is junk. I assumed that by reallocing W, i was reallocing the same pointer as buf. Is this not correct?

**quzah** · 05-20-2005

A pointer lets you change what it points to. Thus, if it's a pointer you need to change, you need a pointer to that pointer.

Quzah.

**hk_mp5kpdw** · 05-20-2005

If the memory pointed to by buf is realloc'ed within the getword function, then the buf argument must be passed as a pointer to a pointer.

[edit]Like quzah said.[/edit]

Code:

int getword(char **W, int size)
{
    ...

    // Resize/repoint the argument to a new larger memory area
    *W = realloc(*W,new_even_bigger_size);

    ...

}

...

// Initial malloc call
char * buf = malloc(INIT);

// Call getword function... afterwards, buf points to new address
getword(&buf,INIT);

**lucaspewkas** · 05-20-2005

cool thanks, that worked

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