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Full Discussion: Segmentation fault when I pass a char pointer to a function in C.
Top Forums Programming Segmentation fault when I pass a char pointer to a function in C. Post 303016290 by dryden on Tuesday 24th of April 2018 02:25:18 AM
Old 04-24-2018
Quote:
Originally Posted by Corona688
It's implicitly a pointer, implemented as one internally, but the same way you're not allowed to change a string's contents, you're not allowed to change its value. Hardcoded.
Those... aren't really similar things. The array's address (the name) is only known at compile time, or debug info, but in the compiled code the 'name' is effaced and you're simply dealing with addresses hardcoded into the code.

Thus, there isn't really anything you can modify unless you were to write the code segment.

The string, I guess it could also be located in a code segment, but more likely is that they are actual data values in a read-only data segment.

As such, the array is not really a pointer, there is no variable anywhere holding its address. So, it's no different from not being able to change the address of some int value that you have defined.

When you do

Code:
char arr[20]; char *p = arr;

That's technically no different from

Code:
int i; int *q = &i;

But I find the biggest annoyance(?) of arrays and structs to be that you can only initialize them at declaration?
 

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LEARN ABOUT ULTRIX

shmdt

shmop(2)							System Calls Manual							  shmop(2)

Name
       shmop, shmat, shmdt - shared memory operations

Syntax
       #include <sys/types.h>
       #include <sys/ipc.h>
       #include <sys/shm.h>

       char *shmat (shmid, shmaddr, shmflg)
       int shmid;
       char *shmaddr;
       int shmflg;

       int shmdt (shmaddr)
       char *shmaddr;

Description
       The  system  call attaches the shared memory segment associated with the shared memory identifier specified by shmid to the data segment of
       the calling process.  The segment is attached at the address specified by one of the following criteria:

       If shmaddr is equal to zero, the segment is attached at the first available address as selected by the system.

       If shmaddr is not equal to zero and (shmflg & SHM_RND ) is true, the segment is attached at the address given by (shmaddr- (shmaddr modulus
       SHMLBA )).

       If shmaddr is not equal to zero and (shmflg & SHM_RND ) is false, the segment is attached at the address given by shmaddr.

       The segment is attached for reading if (shmflg & SHM_RDONLY ) is true. Otherwise, it is attached for reading and writing.

       The system call detaches from the calling process's data segment the shared memory segment located at the address specified by shmaddr.

Return Values
       Upon successful completion, the return values are as follows:

       o   The system call returns the data segment start address of the attached shared memory segment.

       o   The system call returns a value of zero (0).

       Otherwise, a value of -1 is returned, and errno is set to indicate the error.

Diagnostics
       The system call fails and not attach the shared memory segment, if any of the following is true:

       [EINVAL]       The shmid is not a valid shared memory identifier.

       [EACCES]       Operation permission is denied to the calling process.  For further information, see

       [ENOMEM]       The available data space is not large enough to accommodate the shared memory segment.

       [EINVAL]       The shmaddr is not equal to zero, and the value of (shmaddr- (shmaddr modulus SHMLBA )) is an illegal address.

       [EINVAL]       The shmaddr is not equal to zero, (shmflg & SHM_RND ) is false, and the value of shmaddr is an illegal address.

       [EMFILE]       The number of shared memory segments attached to the calling process would exceed the system imposed limit.

       The fails and does not detach the shared memory segment if:

       [EINVAL]       The shmaddr is not the data segment start address of a shared memory segment.

See Also
       execve(2), exit(2), fork(2), shmctl(2), shmget(2)

																	  shmop(2)
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