l i n u x - u s e r s - g r o u p - o f - d a v i s
Next Meeting:
July 7: Social gathering
Next Installfest:
Latest News:
Jun. 14: June LUGOD meeting cancelled
Page last updated:
2002 Jan 31 17:32

The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

Report this post as spam:

(Enter your email address)
Re: [vox-tech] C: functions that return a string
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [vox-tech] C: functions that return a string

On Wed, 30 Jan 2002, Peter Jay Salzman wrote:

> i have a function, GetCPUType(), that returns a local (but static)
> string.  this works from main():
>    char buf[BUFFERSZ];
>    strcpy(buf, GetCPUType(proc_cpu));
>    printf("CPU Type: %s", buf);
> this doesn't (it prints garbage):
>    printf("CPU Type: %s", GetCPUType(proc_cpu));
> the function looks like:
>    char *GetCPUType(const char *file)
>    {
>       static char *ptr;
>       /* do stuff with ptr */
>       return ptr;
>    }
> what's the difference between putting ptr into a buffer and printing the
> buffer vs. printfing the pointer to a string directly?  ptr ends with
> \0.

A char pointer is a pointer... it occupies four bytes, and must be
initialized to point at something.  It does not end in '\0' (that is like
saying one of the squares in a quilt is a sphere), but the memory it
points to may.

A char array has a name, and that name can "decay" into a pointer to the
beginning of that array.

How about something like:

    char *GetCPUType( const char *file )
       static char buf[ BUFFERSZ ];
       /* fill up buf */
       return buf;

but beware of:

    char *GetCPUType( const char *file )
       char buf[ BUFFERSZ ]; /* on stack */
       /* fill up buf */
       return buf;
       /* memory allocated on stack for buf disappears,
          leaving dangling pointer */

Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil@dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
                                      Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
/Software/Embedded Controllers)               .OO#.       .OO#.  rocks...2k

vox-tech mailing list

LUGOD Group on LinkedIn
Sign up for LUGOD event announcements
Your email address:
LUGOD Group on Facebook
'Like' LUGOD on Facebook:

Hosting provided by:
Sunset Systems
Sunset Systems offers preconfigured Linux systems, remote system administration and custom software development.

LUGOD: Linux Users' Group of Davis
PO Box 2082, Davis, CA 95617
Contact Us

LUGOD is a 501(c)7 non-profit organization
based in Davis, California
and serving the Sacramento area.
"Linux" is a trademark of Linus Torvalds.

Sponsored in part by:
Appahost Applications
For a significant contribution towards our projector, and a generous donation to allow us to continue meeting at the Davis Library.