C问题请教:

[jhn]

2000: char * getbuf()
2001: {
2002: char buff[8];
2003: /* unspecified, buff defined here *./
2051: return (char *) buff;
2055: }

1. Is there an alternative, but equivalent, way to write line 2000? If so, what is it?
2. Is getbuf() a reasonable function?
3. Will getbuf() execute at all?
4. Please comment on line 2051.
5. Is getbuf() good practice, and why?

[ACDC]

作者: jhn

2000: char * getbuf()
2001: {
2002: char buff[8];
2003: /* unspecified, buff defined here *./
2051: return (char *) buff;
2055: }

1. Is there an alternative, but equivalent, way to write line 2000? If so, what is it?
2. Is getbuf() a reasonable function?
3. Will getbuf() execute at all?
4. Please comment on line 2051.
5. Is getbuf() good practice, and why?

My 2 bits:
1. Not sure what you mean, it can be written as char* getbuf() ?
2. Not sure what you mean again. Depends on what you want to do with it.
3. It will execute but will cause a memory error.
4. It's returning a pointer to a mem location on stack. The mem allocated
on stack will be destroyed after line 2051 and hence the caller is now
having a pointer to an already 'destroyed' memory cells. The caller may
behave normally most of the time if the over all application is relatively
queisent. But at times it would crash 'mysteriously'.
5. getbuf() does not take any arguments. To return a pointer to the buffer,
it has to either use some global memory or it has to use malloc to get
mem on the heap. Using global is not desirable in most cases. Using malloc
in this context is slightly better if a corresponding function freebuf(char *)
is made available to the caller. My preference would be a function like
boolean getbuf(
char* pbuf, /* IN/OUT pointer to buffer */
int sizeOfBuf /* Max size to fill */
) {
....
// return whether it's success or not.
}

[dongningprc]

A better way to write it:
static char buff[8];

[ACDC]

作者: dongningprc

A better way to write it:
static char buff[8];

I think the use of static would cause a re-entrant problem. i.e. If multiple
processes are using this function, there's a risk of caller A getting a value
that should belong to caller B.

[beastmaster]

作者: ACDC

I think the use of static would cause a re-entrant problem. i.e. If multiple
processes are using this function, there's a risk of caller A getting a value
that should belong to caller B.

each process should have their own copy of this function, because each process has their own stack. and processes only can share something by IPC, but inside each process if there are multiple threads, then maybe will casue critical section problem, need lock to guarantee mutual exclusion. suppose all the codes are in user mode.