shmat() return values?

[Krassimir Slavchev]

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Hello,

When I try:

if ((*shm = shmat(shmid, NULL, 0)) == -1)

The gcc complains with:
warning: comparison between pointer and integer

shmat() is declared in shm.h as:
void *shmat(int, const void *, int);

but 'man 4 shmat;

RETURN VALUES
     Upon success, shmat() returns the address where the segment is
attached;
     otherwise, -1 is returned and errno is set to indicate the error.


What is the correct return value on failure, -1 or NULL?
I think it should be NULL?

Best Regards
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