Question about C code - what is the difference?

[sunroof]

Question about C code

Can someone tell me what is the difference between following 2 definations:

1. char * const buffer

2. char const* const buffer

 

[sxg]

Re: Question about C code

the first one shows the 'buffer' is a constsant, it point to a element of char type
the sencond one shows both the 'buffer' and the context whit char property it pointing to are constant.

 

[sunroof]

Re: Question about C code

what if it is:
const char * const buffer
or
const char * const * buffer

the first one shows the 'buffer' is a constsant, it point to a element of char type
the sencond one shows both the 'buffer' and the context whit char property it pointing to are constant.

So, if I have:
buffer = char packet[8];

for 1), I can change the contents of packet, but can not change the location that buffer points to;
for 2), I can not change any element in packet, neither the location that buffer points to.

Am I right? TIA.

 

[echo47]

Question about C code

Suggestions:
1. Enable all of your compiler's warning and error messages. They frequently catch typos and suspicious code.
2. Search for a small command-line utility called "cdecl". It will translate C declarations into semi-english. For example:

cdecl explain const char * const buffer
Declare buffer as const pointer to const char.

cdecl explain const char * const * buffer
Declare buffer as pointer to const pointer to const char.

So, if I have:
buffer = char packet[8];

You can't have that. It's a syntax error. Maybe you meant this:
char packet[8];
buffer = packet;

If that's true, then:
1. error: assignment of read-only variable `buffer'
2. warning: assignment from incompatible pointer type

 

[sunroof]

Re: Question about C code

Suggestions:
1. Enable all of your compiler's warning and error messages. They frequently catch typos and suspicious code.
2. Search for a small command-line utility called "cdecl". It will translate C declarations into semi-english. For example:

cdecl explain const char * const buffer
Declare buffer as const pointer to const char.

cdecl explain const char * const * buffer
Declare buffer as pointer to const pointer to const char.

So, if I have:
buffer = char packet[8];

You can't have that. It's a syntax error. Maybe you meant this:
char packet[8];
buffer = packet;

If that's true, then:
1. error: assignment of read-only variable `buffer'
2. warning: assignment from incompatible pointer type

Yes, for that assignment, I did it wrong.
It is:

char const * const buffer;
char packet[8];
......
buffer = packet;



Cool~!
I don't know there is cdecl under linux as such a good helper.

But cdecl gives me "parse error" for "char const* const buffer", which I saw a sample code using it.

Any similar tool under Windows? TIA

 

[echo47]

Re: Question about C code

Here is an old DOS version of cdecl that runs ok at the Windows command prompt.
It also gives an error message on "char const* const buffer". I've never done it that way. I guess it's legal. Maybe need a newer cdecl.