Segmentation fault when I pass a char pointer to a function in C.


 
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# 8  
Old 04-22-2018
Yes, I knew most of that. After all, I have Java experience (just kidding).

Well I knew most of that (except the history) -- I didn't know that once it was different.

It's difficult to assess because "segmentation fault" is really about the only error message you ever get :-/.

I'm lucky to know it means "page fault" -- the first time it happened to me I had to think about what it could mean and then I figured it must be read only,

lately I found out that the "const" keyword does about the same thing, but only on the compiler level this time -- but I'm changing the subject a bit I guess Smilie.

Yes, but I often think "An array is a pointer" to remember that I shouldn't use &array to get its address.

But I'm happy to learn this workaround, although I prefer to use strdup("string") instead..... although.... and strdupa also has its own caveats.

Funnily, in Java Strings are also immutable, and you have to use StringBuffer (or StringBuilder) instead to change them. Because of that reason, porting from C to Java is sometimes less strange than you would expect.

I'm actually quite interested to start using that garbage collector though (libgc1c2), although the number of applications (on Linux) that actually uses it is rather limited, only Inkscape depends on it on my system.

Anyway, enough.
# 9  
Old 04-23-2018
Quote:
Originally Posted by dryden
Yes, interesting. So because that array stores actual memory on the stack, you cannot change what it points to, hmmmm. I thought arrays were pointers, until I tried to assign an array (pointer) to something else ;-). [I mean the reverse, assign something else to that array].
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.
# 10  
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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